if you are up for autocross than its best if you get some coilovers and some good tyres with custom alignment...you might want to visit zafcom tyres gizri for alignment and tyres since he works on a lot of autocross cars. After that you might want to invest in suspension parts such as camber plates, strut bars, lower control arms.
In autocross its all about how well your car is balanced and how good the suspension is. Power is secondary. Just slap on a taiwan intake and get 2.25" straight piping done from Saleem (Lucky silencer) at gizri, it will be minimal gains though.