You're not going to want FA with /DA, the end drain is fairly large, and with IO's the +ToHit is less useful. However, the body mastery pool might be worth dipping into, just to get CP.
As for tough, I'd say it depends on whether you use CoF, that's a farily large drain and I don't think you'll want any more toggles if you do. If you don't, tough could be quite a nice addition.
There's also the possibility of taking the ST hold from dark, which, combined with end drain resistance from DA would make you a good sapper neutralizer. But then again, you already have headsplitter and disembowel for that 
My Scrapper is an Oppressive Gloom sort of girl, rather than CoF, and my endurance is just about manageable these days - especially with some +recovery bonuses. If I can get some knockback protection and get rid of Acrobatics, even better.
Tough is sounding awfully tempting, although a hold would be useful. Not as fun as just jumping in and "arresting" the bosses with Headsplitter though.
spidermonster.
Tough and conserve power are nice picks 
thePhilosopher Martial Arts/Regen/Fire Scrapper
theRegulator Empathy/Energy/Soul Defender
Total Inertia Ice Blast/Kinetics/Psy Corruptor
Total Inferno Ice Blast/Thermal/Leviathan Corruptor
About that boat load of psi damage coming up.. Id get taunt to properly challenge the psi AVs.
He will honor his words; he will definitely carry out his actions. What he promises he will fulfill. He does not care about his bodily self, putting his life and death aside to come forward for another's troubled besiegement. He does not boast about his ability, or shamelessly extol his own virtues. - Sima Qian.
With the acc bonuses of crushing impact, FA may be redundant and as stated, is a huge end drainer, Conserve Power will be extremely useful on a DA scrapper and I personally think Tough will be also immensely useful if you can manage the end, unfortunately, the +recovery unique enhancements are awfully expensive.
It would be helpful to try the respec on the test server and see how it goes.
I have tough on my DM/DA and as pointed out in my guide, with tough and some good slotting you can get near the scrapper cap on S/L damage.
I'm dropping Body mastery to take Dark mastery as I've found my self using CP less and less. With good slotting and invention sets, I'm finding I don't need FA. LaserBeem eyes is the one I use the most.
I think the Dark Mastery powers work better with my concept, play style and teams.
So I'm hitting 40 tonight with my BS/Dark Scrapper, and then will be into AV and epic storyline territory.
During the 40-50 stretch, there'll also be the last few power picks (as well as getting some knockback protection IOs, if I can afford it, and losing Acrobatics) and I'm not sure what to take.
I was originally thinking of getting the Body Mastery pool, since FA would be useful... but I've got a plan to have quite a few Crushing Impact sets in my attacks (five sets of it, in fact - if I can get it all over and over)... which'll give me a nice accuracy bonus once they're all in place. So FA would be a bit redundant.
None of the others really appeal, for concept reasons, though I guess Darkness would fit.
The only other real contender is to go into the Fighting pool for another attack, and Tough.
Does Tough make a noticeable difference for /DA in the 40+ game? That's my main question.
I've got well-slotted Dark Embrace and Murky Cloud already, of course. And am adding more slots to Obsidian Shield since I know there's a boatload of psi damage coming up.
spidermonster.