I disagree with your line of thinking.

If poor people are deterred from speeding because of the cost of the fine, then why are we talking about poor people getting fined at all, after all they wouldn't be speeding.

Just because someone has money it does not mean they will flaunt the law because they can afford the fine.

In both cases correlation does not imply causation.

Where demerit point systems are in place both poor and rich lose their licenses after too many infringements.