Getting more Power!!!

[xnamerxx]

I'm looking for some info on getting power out of this car per the STF rules. Going through the posts for the past year hasn't really netted me the results I was hoping for.
I'm fairly limited into what I can do, essentially I can tune the car as long as it plugs into the stock harness. I can replace the header and swap the cats to high flowing cats (100 cell limit). I can change the intake all the way up to the throttle body but not the TB itself and I can change the pullies with over/under driven pullies. From going through the forums it seems like I'll never break 105-110 whp with the above limitations which makes it almost not worth the money/effort.
Can someone give me some real world examples of what the DC header or a tune does for power? I feel as if I'm grasping at straws trying to get any power from the car.