To make any signifigant gains eventually you'll be looking at a motor swap, and more or less have to strip the car. Getting a different car is really the only practical thing here. Little things like exhaust, intake, and a tune can be done, but you're looking into four-figures dollar wise for decent stuff, and you'll only get a barely noticable gain, not even close to worth it IMHO.
You wanna get faster? I highly recommend AutoX racing. It's one car at a time on a course made of cones; no danger of crashing into anything. There are different classes for different cars, you're not competing against Vettes. you'll be trying to beat the times of Grand Ams. and there is a novice class for beginners. It costs $25-$40 a day. The biggest organization for this is the SCCA which runs hundreds of events across the country, although there are other groups that do races as well.
People have no idea how much skill racing takes, even in a slow car. Go to five of these events, take in all the advice from the pros (maybe ride with them on a run or let them ride with you), and I'm betting you'll knock 1/4 off of your time. To do that with modifications would have cost you thousands and you'd still be a shitty driver.
Submitted for the approval of the Midnight Society