If you've got big plans I say get a better base vehicle. If you just want to spice it up, exhaust is the way to go. Good tires wouldn't hurt either. You could do a SMALL shot of nitrous, but that would be risky if this is your daily driver. Also, nitrous is a pretty good deal if you're running a 150+ shot, but to run a 25 shot you need pretty much the same equipment, making it not that good of a value.
Submitted for the approval of the Midnight Society