I don't even see how this is even remotely possible--are you letting people win bids with zero coins? That should never happen--at least not after your first game when you're learning the system. By the published rules, you only get 1 coin per tile--the only way you can get "richer" is if you pay nothing. If you even pay 1, your net gain is zero.
I agree with most of what you said although I would perhaps quibble and say that if you get a tile for 1 coin in the first year it generates revenue in all subsequent years, so it is ultimately worth 4.