As for my Spec V, I started with:

1. CAI from Injen - very little power gain, but my fuel economy went from 28mpg to 30 mpg on the highway.

2. Catback from Stromung - nice power upgrade, more hp and torque, and the spec v has a nice rumble from the exhaust. You opt for the resinator if you don't want to hear the exhaust

3. Lighter wheels - Stock wheels weigh 25 lbs each, I bought some Enkeis that weigh 19.5 lbs.