Where are you at? A stock Evo X here wouldn't really be competitive at all in STU.
Your AP is legal -- just the maps that are provided are not. You can use ATR to make changes/log a tune that only changes timing, fueling, and MIVEC (no boost). You'll need a wideband though.
My recommendations for low buck mods?
- brake pads
- $25 camber bolts. You flip the top bolt like on the VIII/IX to make the paint dot away from the strut (~-2* camber). Then you put the eccentric bolt in the bottom and you should be able to get to about -3*). (
http://www.clubrsx.com/cr/SPC-81260.html)
After that... it's a tossup. Two schools of thought, springs/sways, coilovers/sways. The front sway did more for me than the rear sway, but it was 4000x harder to install.
Other things you can do and stay legal in STU:
- intake
- exhaust (full turbo back, but you have to keep a cat)
- stainless brake lines
You should also consider a CG Lock or a harness to help keep you in the car.