I raced SCCA Solo II for a couple of years and loved it. Been 15-16 years since I last raced, but I still have the friends I met then, the knowledge I gathered and some really really cool pictures!!!
Check with your local sports car club. Many local clubs have autocrosses and establish different rule classes. My local club did (and still to this day continues) to allow some modifications or a group judge agreement on where a car should be placed in classes. They did a point system. Wheels/tires were 1 point, modified exhaust cat-back - 1 point etc., and with enough points you moved from "stock" to "street prepared" to "prepared" and finally to "modified". Modified would be a car that could never be a street car like a Formula Atlantic etc. Worst you could do with a "door slammer" would be "prepared." Then the cars were broken down into groups based on speed. The idea was to keep the classes competitive. And it worked. The distances between the slowest experienced driver and the fastest ones in each class was only a few seconds. It was terrific to watch your driving skill improve each race by seeing how close you were to the fast guys.
Point is, that you should check to see if your local club has a place to put such vehicles as your speedie. In our club, it would have run with the slower cars (compared to say a Dodge Viper or a 930 turbo) in a street prepared class against others of a similar speed.
As far as "thrashing" the car goes, well, don't confuse "thrashing" with driving hard as they are two different things. Smooth drivers do not break properly engineered cars in an autocross. If your car is in poor tune, has a hand-grenade for an engine, you can't shift or there are monkey rigged parts you're gonna find them the $$ way. Otherwise, trust me on this, drive well with a sound car and you will drive the car home every time. You will run over cones and may scuff the finish, spin out occasionally and run the rear tires ragged (adjust pressure PRIOR to your run). And you'll have a BLAST!
angela