I'm not sure used cars are really a good addition. Seems like a way to cheat to me. Ex. The Skyline GTS-t Type M (R32), with ~80k km has 220hp. The same Skyline in GT3 (if I'm not mistaken) also has 220hp. Also, some cars cost more with fewer miles, while the same car with more costs less, but has the same power. I wasn't talking about a few thousand km either, it was at least 30k.
Looks like a way to cheat to me. I'll be taking that R32 for a starter, though.