No, it is a bad idea because it is bad idea. It is an arbitrary and, quite frankly, stupid restriction on one of the game's features, and one that no other game that I've ever heard of that offered similar features has ever done. It doesn't "encourage" car collecting. It extorts you into doing so by making one of the game's features completely useless unless you do so. What's next? Are we going to have Pokemon-style broken bridges that outright prevent you from proceeding in the game? Like you can't enter certain races unless you buy all of the Skyline variations?
Explain to me why it is better to force you to hunt through the used cars lists for a car in a color approximate to what you want, and then force you to do so again after you repaint one car (you see, that's the real kicker. I could almost understand the point behind it if you kept those colors forever after getting them once, but the way it seems to be is just inane). Explain to me how imposing such ridiculous restrictions is better than, say, offering an RGB map and allowing the player to choose whatever color they want for an in-game fee. You know, like nearly every other game ever made with a repaint feature.