It would help focus peoples' minds on the harmfulness of speed if, rather than setting arbitrary thresholds, the fines were proportional not only to income, but also to the excess kinetic energy of the vehicle:
Ek = 1/2 . m . v^2
Kuisla was doing 65 in a 50 zone, so his "kinetic tariff" would be (65x65) - (50x50) = 4225 - 2500 = 1725 units. (It's the exponential nature of the velocity squared factor that yields the disincentive, but, by all means introduce the weight of the miscreant's vehicle too)
This would be a rational way of reflecting the a) the risk of injury in the event of a collision; b) the undesirable environmental effects (noise, gaseous emissions), both of which rise exponentially with the kinetic energy of the vehicle.
This kinetic tariff can then be applied to income data to calculate the actual fine for the individual.