i've also been rolling this question around in my head. i have a 18 spines/wp, but i've done wp a bunch redside, and i imagine jumping around tossing metal spikes whenever i feel like it may not necessarily vibe with rttc.
this question has come up on the boards more than a few times, but im interested in people's takes on it again.
50s:
Grimmloch, Tactically Delicious, Ugly Frankie, Operative Tracker, CryoFurnace, Professional Help, Silver Sphinx, Aries Knight, Tachyon Aegis, Jade Sphinx
Currently building:
Any one of half a dozen alts!
DA pros:
dmg aura
self heal
stun aura
cons:
end hog
no kb protection
lots of slotting devoted to typed defense
no dmg boost
Fire pros:
dmg aura
end boost
self heal
dmg boost
cons:
end hog
no kb protection
lots of slotting devoted to typed defense
Electric pros:
dmg aura
20% recharge
end boost
end discount/heal/regen
low end cost
cons:
lots of slotting devoted to typed defense
no dmg boost
My take on it:
WP - good pairing because it synergizes with powers like spine burst and quills that puts you right in the middle of the action. It also solves how endurance unfriendly spines can be, since you have access to quick recovery. Probably the most synergistic choice.
Regen - great for an almost all ranged concept where you don't take spine burst and quills but go for a ranged attack chain (throw spines, impale, 2 epic ranged attacks with the occasional ripper). It works because +rech you get for regen helps you spam a lot of cone range attack at range. Built well, the combination can be extremely tough since the +slow in the spines attacks provide decent mitigation as well.
SR - a good solid secondary for spines. Lots of mitigation (especially soft capped) allows you to choose a play style that it's either PBAoE centric or mostly ranged. Spines can be endurance unfriendly, so this build will need some help with recovery. The innate +rech of quickness works well to get some of the slow charging spines attacks available more quickly.
Dark - built for PBAoE damage with quills and the dark armor auras doing most of the heavy lifting. Was considered almost unplayable without carefully managing toggles back before IOs. Now, while it is still endurance expensive, IO recovery bonuses make it much more manageable. With a lot of IO investment, it's probably the strongest spines combination (IMO).
Fire armor - a concept much like dark armor but with a higher damage potential with fiery embrace and blazing aura thrown into the mix. However, it's arguably the squishiest of the spines combinations. While the combination sounds great on paper, it probably lags behind a well built spines/dark, since you trade away a lot of survivability for greater damage output.
Electric armor - about as squishy as fire armor I presume but with no endurance issues, the ability to sap endurance away from foes in long fights and lightning reflexes providing innate +rech. The small heal lags behind what fire and dark armor gets. Still, it has some nice extras such as a near immunity to end drain and energy damage, which are nice things to have in the end game. I haven't played this combination so these are presumptions based on what I know of electric armor in brutes.
Should mention that I only really have experience with spines/fire and my list is largely just my take from glancing at the power lists in Mids.
I too am going to keep watch on this thread.
I have a solo, level 21 Spines/Willpower I am loving. I don't know if it will really help much in keeping the bad guys around me, but I threw a Taunt Common IO into RTTC.
An almost all ranged concept sounds interesting for Spines, especially now with Blaze Mastery. Don't take Spine Burst or Quills you say...hmm...actually, when I get into the 40s, I can see myself doing this. I already deeply regret taking Quills before I took Quick Recovery, and Spine Burst right now is meh. Of course at 22, I do not have the slots to properly slot everything that demands a lot of slotting.
So far, one of my fav Spines powers is the power everyone says never take. Forget what it is called...Barb Swipe? At level one you have two choices, Lunge and...it. This power looks it is rubbing in the poison, and it never fails to make me laugh. I am hoping to be able to keep it.
Good luck with your Spines 
Lisa.
So don't wait for heroes, do it yourself
You've got the power
winners are losers
who got up and gave it just one more try
***Dennis DeYoung
Barb Swipe is nice to start out with, but like most short-animation low-damage first attacks it gets used less and less as you develop an actual attack chain. Lunge will be fine once it gets some recharge from slots or set bonuses.
First person I've ever heard use barb swipe and short animation in the same sentence without some negative descriptors thrown in.
With the changes coming to Spines in I-16, I decided that I finally want to try one. The problem is, I really don't know what secondary to pair it with. I was leaning toward Dark Armor of Fiery Aura, since Dark Armor has some good AoE utility and Fiery Aura can offer protection while also helping AoE damage output. But I also know some of the other sets have gone through some other changes, and as I only really have experience with Regeneration, I was wondering what you all thought.
Thank you!
Characters I am Currently Working on:
Corcra Dragan - MA/Regen Scrapper (Hero) - Virtue
Chronian Phoenix - Time/Fire Defender (Hero) - Virtue
Mindzeye - Psy/MM Blaster (Hero) - Virtue
Valence Vixen - Elec/Elec Stalker (Villain) - Virtue