So you somehow think that the $300 fine deters or hurts the person making $200k a year the same that it does the person making $20k per year?

It's not that the poor person speeding is any less dangerous than the rich person speeding, it's that the $300 fine doesn't really matter to the rich person. It's just a price they're willing to pay on random occasions to go faster.

We already have points as a wealth-invariant mechanism to affect drivers. No one has demonstrated that a flat percentage of income has a flat response curve. Given you already have a wealth-invariant mechanism, the fact that you are trying to add something else makes me think it’s not about wealth invariance.