BIAS NOTE: All information comes from a Kat/Will scrapper
1. Willpower is fairly survivable
2. Willpower works well 'out of the box'
3. Unknown, although I assume willpower can be turned into something truly frightening with IOs.
4. I personally have it off as often as I have it turned on.
5. You have a good mix of defensive types, but none of them are in themselves overwhelming. Overestimating your abilities leads to death.
6. I have no idea.
7. I have no idea.
8. No.
I can answer a few of your questions and add some anecdotal evidence:
First of all, RttC caps at 10 enemies. It still is quite noticeable with only a couple. In reference to Scientist 16's post, I have a Claws/WP scrapper at 43, and I currently run the following with only slight endurance issues (Mainly because I don't have very many sets yet, only 2 atm and no Numina or Miracle):
Mind Over Body
Indomitable Will
Rise to the Challenge
Heightened Senses
Maneuvers
Tactics
Assault
Hover
In terms of survivability, you'll notice less "rubber-banding". You have higher defense and resistance, but lower regen. As such, you'll take less damage, but you'll also regen it at a slightly slower pace. The only problem that I find with Willpower is that it does not have a clickable "Oh S**t button" or a click heal. The final power is more of a "This looks like a huge group, I better preemptively use it" power.
To make a long story short, you don't have to worry much about your secondary if you take willpower; it is very passive. You can really focus on scrapping it out, which some players like and some don't.
1: How survivable is WP?
Much more so than Regen, esp. in the late game. You have a mix of resistance, defense, and regeneration, all on toggles or passives, so you are less likely to get clobbered.
The tradeoff is that WP is a chore to get to 22, like any other set. At 22, you should have both Quick Recovery and Stamina, and the world is your oyster.
2: Does it need heavy IO slotting to really shine, or can it do well out of the box?
Does fine out of the box.
3: If it does need IOs, how much money should I be looking to spend?
I'd say I've spent maybel 50-60 million on my level 50 Spines/WP scrapper. Mostly just to beef up the offense, and Spines accepts stuff that's inexpensive and off the beaten path for melee, so I use frankenslotting when it seemed advantageous.
I have not been single mindedly pursuing defense bonuses like I did with my Dark/Reflex scrapper. Don't feel a need. I went for +hp and +recharge instead. This is a viable strategy, but more costly.
4: Is one capable of doing well even without 16 people cramming around you to fuel RttC?
Yes.
5: Any particular weaknesses that I really need to watch out for?
It is somewhat vulnerable to big incoming damage, but not to the same extent that Regen is.
6: Is it possible to cap defense? If so, would it be typed or positional defense?
I've seen it done. Not my thing, though. Never felt the need to on my Spines/WP scrapper; she has too many other forms of mitigation going on, and if she gets over her head she has the option of jumping out, knowing that she will outrun the mobs.
If you go BS/WP or Katana/WP it can be done without any problem at all.
7: How much Regen can I can, both in and out of RttC?
Mine was somewhere in the low 600% level with three mobs around last time I checked.
8: Does playing the Super Mario invincibility theme have any effect?
It's playing all the time around here.
<《 New Colchis / Guides / Mission Architect 》>
"At what point do we say, 'You're mucking with our myths'?" - Harlan Ellison
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1: How survivable is WP?
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If you know anything about Arcanaville's secondary effectiveness spreadsheet or even care, */WP get's substantially higher than average values for virtually all conditions and oftentimes best or second best survivability. It's one of the top contenders, especially when you've got IOs backing it up.
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2: Does it need heavy IO slotting to really shine, or can it do well out of the box?
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Like every Scrapper secondary, IOs just make it more devastating, but, unlike others that you may think of (SR and Shield), even without IOs, it's still one of the top secondaries.
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4: Is one capable of doing well even without 16 people cramming around you to fuel RttC?
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It's a bit weaker than Regen with only a single target for RttC fuel, but it's still better than average. Remember that RttC will give Integration level +regen with only a single target, so it's not insubstantial even at its lowest.
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6: Is it possible to cap defense? If so, would it be typed or positional defense?
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I've seen both though much can depend on your primary and how much of your attack string you're willing to sacrifice for it.
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7: How much Regen can I can, both in and out of RttC?
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With single target RttC, you will have as much regen as you had on your */Regen without Instant Healing on. With saturated RttC, you'll have regen nearly twice as high.
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Sorry about my loads of questions, I just really don't want to suck.
I'd feel stupid if I rerolled a character from a badass to something...less badass.
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Depending on what you do with that */regen and how fast you are with your reflexes, and how interested you are in keeping that fast paced style of play, you may find that */WP outperforms your */Regen rather much, especially with IOs. */Regen gets a remarkably small amount of added survivability and functionality from IOs. */WP gets a significant amount.
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Sorry about my loads of questions, I just really don't want to suck.
I'd feel stupid if I rerolled a character from a badass to something...less badass.
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So long as you don't reroll into a completely different archetype, you're not going to suck. No scrapper combination sucks (although I'd be careful about rolling electric armor scrappers: I doubt they will suck either, but they will be tricky to squeeze comparable scrapper-level mitigation performance out of).
I'd say that Willpower has slightly higher potential than Regen, but there are playstyle issues to consider. Regen has strong heals which means it tends to encourage players to push a little beyond the set's capabilities, provided there is a heal available to bail you out of. Willpower has +regen but no heals: if it gets in trouble its options are inspirations, and running. However, Willpower is less likely to get into trouble in the first place all other things being equal.
I emphasize "all other things being equal" because they often aren't: scrappers tend to like to push boundaries, which means what often matters is not how strong a powerset is, but how well it deals with being pushed too far. What I mean by that is that if there were two scrapper secondaries, and A allowed you to take on 12 things at once, but 13 would probably kill you quick, and B allowed you to take on only six things, but if you tried to take on ten it would hang in there for quite a while before breaking down, a lot of players would instinctively suggest that B was far stronger, even though in this case numerically speaking A is vastly stronger.
In this case, I believe given comparable expenditures in build Willpower is going to be stronger than Regen, but a Regen player transitioning to Willpower might die a few times before realizing they don't have that emergency button heal and not pushing as hard as they would a Regen. They'd be soaring at a higher level if they adjust to the playstyle difference though.
[Guide to Defense] [Scrapper Secondaries Comparison] [Archetype Popularity Analysis]
In one little corner of the universe, there's nothing more irritating than a misfile...
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I have both and willpower is a lot more fun. I do a lot of testing with the MA and just spawning all AVs and it's a lot more survivable then my regen scrapper. although the wp one is db and the regen is katana.
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numbers crunching is pathetic! I play for fun.
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LOL. I crunch numbers for fun.
"That's because Werner can't do maths." - BunnyAnomaly
"Four hours in, and I was no longer making mistakes, no longer detoggling. I was a machine." - Werner
Videos of Other Stupid Scrapper Tricks
Such a sig in the scrapper forum should be considered trolling. 
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Such a sig in the scrapper forum should be considered trolling.
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I wonder what people think about mine when I post in the other AT forums.
"All problems can be solved by throwing enough scrappers at it."
@Riez on Virtue, Protector, Champion, and Exalted server.
Why reroll? Have both and make up your own mind.
Why reroll? Well, unless you can provide me with a way to have two characters with the same name, I'm afraid that's going to be the why, sir!
Aside from that, though, thank you all very much for the info. Looks like a reroll to /WP will do just fine. Now to respec and hand all his stuff over to his new incarnation.
Wish I could get Mid's to work.
Different server. Problem soved! 
Alternatively, pay for a rename of the old character.
"That's because Werner can't do maths." - BunnyAnomaly
"Four hours in, and I was no longer making mistakes, no longer detoggling. I was a machine." - Werner
Videos of Other Stupid Scrapper Tricks
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See topic. I have a 46 Fire/Regen Scrapper that I may reroll into MA/WP, given I16's announcement of animation customization for MA.
[/ QUOTE ]Make both.
And as for comparing /regen to /wp...
If you are a bad player who does not like thinking, /wp is way more powerful than /regen.
If you are a good player who likes thinking, /regen is way more powerful than /wp.
Meh, they're about the same: easy-mode or easy-mode ultra.
Winner of Players' Choice Best Villainous Arc 2010: Fear and Loathing on Striga; ID #350522
Then their is the chance you'll pvp, and reg>wp there, way more survivable and you don't need lol aidself. Regen by far is one of the if not the hardest thing to kill in pvp.
The funny thing is, even though you seem like one of the whiners that got the changes made in the first place, you're probably still bad..------Macskull on Crop_of_shaolin
http://ravens-wins.mybrute.com
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Why reroll? Well, unless you can provide me with a way to have two characters with the same name, I'm afraid that's going to be the why, sir!
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Use caps, substitute zero for a O, use a dash, add a space.
I've dropped down to mostly 2 characters spread across about 12 different builds 
See topic. I have a 46 Fire/Regen Scrapper that I may reroll into MA/WP, given I16's announcement of animation customization for MA. My biggest concern, however, is whether or not WP is a suitable replacement for Regen.
1: How survivable is WP?
2: Does it need heavy IO slotting to really shine, or can it do well out of the box?
3: If it does need IOs, how much money should I be looking to spend?
4: Is one capable of doing well even without 16 people cramming around you to fuel RttC?
5: Any particular weaknesses that I really need to watch out for?
6: Is it possible to cap defense? If so, would it be typed or positional defense?
7: How much Regen can I can, both in and out of RttC?
8: Does playing the Super Mario invincibility theme have any effect?
Sorry about my loads of questions, I just really don't want to suck.
I'd feel stupid if I rerolled a character from a badass to something...less badass.