You can move up to a V8, but if you live where I do it will cost you more for the car, the insurance and the gas.
If you want to stick with the v6 and you can spend the money on the super charger it is kind of a no brainer. You do save some money compared to a v8 and the v6 weighs less so it is nice deal.
If you don't want to spend $6-$7k on a super charger then you can make some mods.
I personally don't want a V8 at this time and I don't have the money for the SC, so I started with the CIA and Tune and I am very happy. the set Up I got boasts 20hp and 30 ft/lbs for $700.
If you re-gear the rear you will improve your mechanical advantage and just about everyone that does is it seems to be really pleased. Good luck getting a consensus on which gear ratio is best. You will more then likely see some drop in your gas mileage, but a minor improvement in gear ratio does not seem to be all that noticeable.
I will probably re-gear at some point.
You can also free up some HP by going to an Aluminum Drive shaft, Lighter weight rims, LW Hood, LW Trunk, Eliminate your back seat, LW Rotors, etc.
Aftermarket exhaust can flow better and sound better, especially if you are flowing more air into the motor. It seems as though there is also some weight to be saved here as well. Of course good luck figuring out which set up is the best, most people tend to pick their exhaust based on sound. The issue is also complicated by the fact there there is several sections of the exhaust system that can be replaced, so you have to decide how much is worth it to you. AND if you live in a state like my home state of Kalifornia, a lot of the these products are not "SMOG" or "C.A.R.B." legal, so when you take your care in for smog testing and inspection you have take it all off and put it back to something legal.