Unless yourgoing extreme (suprcharger), you won't get much more power.

For a little more response an exhaust and induction kit (or modify air box, lots of drilling and panel filter). Gives the car a good V6 roar.

I'm quite happy with my Scorpion exhaust (single tailpipe 2 silencers instead of std 3) and K&N induction kit.

Personally i'd concentrate on the brakes as i think they are shocking as standard. I've now got braided brake lines, DOT 5.1 fluid, National Sport 8 groove disks and Ferodo DS performance pads and very impressed with the improvement.

Good luck.