I'm new to following this type of racing, but what initially drew me to it (as opposed to Indy, F1, Nascar or any spec-racing series) is the variety of cars.
As long as there is some variety I'll continue to follow it.
Maybe 2 GT classes, one stock-ish and one very unrestricted, some kinds of prototype classes that also allow for experimental/hybrid/TDI/Deltawing, etc....
I think that the experimental stuff, exhibition or competitive, is an important element of this kind of racing. As in, I like to see it personally :)