For the 2004 and up models, Turner is coming out next month with a Conforti software upgrade. An intake, this software, pulleys, a more aggressive differential, and an exhaust would be the best bolt-on performance mods you can do. Headers and cams would also be a great upgrade but will cost more to install than the above items. Exhaust and headers will obviously make your car louder, so plan on that. Also, headers require some extra labor due to o2 sensor fitting, so if you're not doing it yourself, it will be pricey.
Regarding the supercharger, sure...if you have at least $5-7k available to spend, that would give you the most gains. However, most of us who only come up with $200 or $350 at a time every so often, the above mods are the most practical and yield some gains (which realistically, are not THAT much...but noticeable at the butt dyno). Good luck.