Alternative versions of cars
It would be a nice consolation prize for spinning several times the same cars: as soon as you get your fifth Aspire (for example) you unlock an alternative version of it with the same shape but a different color. You could make two different alternative versions, one to be unlocked the fifth time you get the same car, and the other the tenth. That way you always get something nice when you spin!
A shiny version (gold version) could be great to XD
I think this should be great to unlock a "gold" version of a car after using it a lot like making 100 races with one car or something like that.
the players will be encouraged to play with all the cars if they want to unlock the gold version