Not sure how much luck you'll get chasing 150kw... there's not much out there for N/A engines aside from exhausts and intakes (unless you want to start talking thousands of dollars, but that's getting into conversion territory), and they don't really give huge gains either. Main reason people go down the path of selling for a WRX or converting to a WRX/STI engine.

Luckily there's plenty in the handling department... WRX 4/1 pot brake set-up does wonders, and you could pick up a set of coilovers or STI struts and springs and drop them in for better handling. Sway bars can be done but something has to be changed in the rear so you have the mounts to attach them up... can't remember what exactly but it's a matter of swapping two bits out for WRX items or just having a bracket welded on.