#1 thing for willpower is to throw out the window the stereotype that Willpower is for psyker stuff only. I'd argue that one can be brave enough to be able to keep fighting under fire, but lack the willpower to resist pulling the trigger at the closest enemy instead of carefully selecting targets (imagine a Goliath having a good scrap, will he really bother picking targets for his bolter?). Also Willpower seems perfect to be able to deal with long term trauma. For that I've redone Injury table and "grievous injury" makes your fighter start with a flesh wound, unless he passes a Willpower check.I'm not so sold on Willpower for target priority checks, its described as the ability to remain cool under fire and not panic and just shoot the closest target. Cool seems right for it.
I'd argue intelligence and willpower need one or two more niche uses each.
As for intelligence, make 1 or 2 "core" scenarios that use intelligence for objectives and intelligence becomes more interesting. Another idea to revive intelligence that I've tried (and which is working!) is to let people draw 1 tactical card whenever they open a loot casket. This way, smart and mobile gangers can get tactics for their team (strong gangers can do that too, but have a higher risk of exploding in the process).