I'll add that it could create some really perverse incentives. Small town cops encouraged to pull over any newer or more expensive car and ignoring ones that look janky.
I would argue that fixing that is important, even without income-based fines. Particularly if you have things like civil forfeiture (which also needs some fixing and really sounds like something that belongs in a banana republic).
They also don't have the government sanctioned theft through the ridiculous notion of civil forfeiture...