No, the selection of cars is not boring to me. I've been doing it for years and there are still cars that I have never driven.
Some cars I'm more interested in than others, but that is largely dependent on which car/track combos are popular online, or some league event that I've joined.
I get the feeling the OP hasn't really dug deep enough to be able to appreciate the characteristics of each car, but then again, I wouldn't know, maybe he does it all offline.
About the "are just variations of the other cars" comment: yes, they are, aren't they, all have 4 wheels, an engine, a spot for the driver to sit, and some kind of linkage to steer the front wheels.
How about rear wheel steering? Or a hovercraft? Now, THAT would be different.
Btw, love your avatar, Hankstar.
Ok, I admit, there are silly bits in my post. Sorry....