Of course this could be fixed by means-testing, CART charging a lower license fee to those on low incomes or the unwaged, and more to those who are much better off. I can't see there being any objection to that, or opportunities for fiddling the system... 😉
A much simpler approach -- far less admin effort, no privacy issues, and harder to fiddle -- would be to charge by boat age, say going from 1.5x for "new boats" through 1x for "typical age" boats (12yo?) to 0.5x for "old boats (25yo or above). Which would solve the problem for low-income people like LadyG and others who tend to have older cheaper boats, and get more money from people like me with new shiny boats -- who must have been relatively well-off to buy an expensive/new(-ish) boat in the first place.
Couple that with area-based charging and a bigger CC surcharge (+50%?) to make up for the money CART don't get from CCers compared to HMers, and surely everyone would be happy, including LadyG? 😉