Right now, there is a hard limit for any kind of vinyls a player may add to a vehicle.
Now, I'm not sure, but there may be a technical limitation to this.
The way I've been thinking it should work is that the vinyls be separated into two categories: basic vinyls and graphics.
"Basic" vinyls include shapes and simple body vinyls. The player may apply a theoretically infinite ammount of these (or at least a high cap). To compensate, basic vinyls would offer little star rating*, as their purpouse is for the player to create designs of their own with a selection of geometrical shapes, letters, numbers,... with gradients and without,...
Plus, the player could modify these extensively even by skewing them, which is not possible right now (limitation?)
Graphics would work just like they do now, special designs that boost star rating* significantly. The player may apply a limited ammount of these, and they would be unlocked by recieving vinyl points through special events.
*The star rating mechanic is an unnecessary carryover from Underground anyway and I wouldn't mind if it was removed entirely.
Instead of taking those annoying covers that just sit in your dumpster how about making those events "open world time trials" (Midnight Club style) and just having a photo mode the player can use anywhere, the covers page would be a photo album.