a CAI will make the car breathe a bit better, but if you want to do it properly - get a heatshield made to stop the hot engine bay air, getting sucked into the intake.

I can says from what i've seen with my own eyes on a VtiR, a CAI, exhaust and a VAFC which was dyno tuned - gave my mate a good 10HP@wheels and you could feel it!

Which ever way you look at it, those are basic 'mods' on most cars, so sooner or later you're bound to do it anyway