I have a 2000 Caterham Superlight #123. There are plenty of classes for other cars to run in, depending on the state of mods that have been done. There are even a number of street tire classes.
Seven's unfortunately by their very nature are too capable/fast so the SCCA forces 7's into the Modified class, where almost anything goes. My Caterham is bone stock, same springs shocks etc. that it comes with from the factory. However, tires are the difference, in Mod, you can run full slicks. That's where the biggest difference would be.
That being said, I ran street tires for the first several years, and its still fun. It's really about driving your car to the best of your ability first, then beating the competition/clock second.
We have some very good instructors who would be glad to ride with you to help you improve.
Come on out, Have fun, and drive your car. :7fume: Tom