I don't think income is related to speed. I speed for one reason: I'm impatiant as all hell. I get mad if I'm not travelling at least 10 kmh over the posted limit, and my patients is not inextricably tied to my income.
Tying someones salary to the traffic offense is a little silly as well. Where do you draw the line? On fines? On criminal traffic offences? Stunting isn't illegal, but it's the same as a DUI on your abstract.
Cop: Did you know you just ran down a small animal, took out 3 hedges, and blew 0.20 on my breathalyzer?
Me: Sorry about that. BTW, I'm on welfare.
Cop: Oh. My mistake. Here's your 50 ticket.
Me: No apologies necessary, can I have my keys back?
Stuff like that should be on an equal playing field. If you can't afford the ticket, don't speed.