I had an 02 RS and this is what I had attached to it:
-Cobb headers + High Flow Cat
-Cobb Cold Air Intake
-Cobb Power Pulley
-Strumong dual-tip exhaust
-Gold coated engine ground kit.
-WRX Aluminum Hood
-Front and Rear Sti Rep. Strut Bars
-Cobb Rear Swaybar
I'm don't have any numbers or dyno charts, but my Butt dyno really liked the extra added power/low end torque that all these parts together did for my little 165HP RS.
Good luck with your modding. Just take it easy because you can spend a ton of money in no time: