I appreciate your predicament. Me buying one probably doesn't help.
Is it economically feasible to include the owners license plate or racing numbers on the car? That may spur additional sales. Recreating every state plate could be a real pain, so possibly just do a Euro style plate. The same with racing numbers, just use a big white circle with black numbers. The main thing is it would be personalized.
I would also suggest giving the designs more descriptive names. Instead of "Billy Bob's GTS", how about "02 GTS, Graphite, no Stripes, Rear View"? As it is now, it requires a lot of searching to see if "your" car is there.