Does it need to be addressed? On Hard difficulty I seem to have gold coming out my ears!
How many people are in your Kingdom/Empire currently?
I've been speculating that in the late game, Gildar would be coming in pretty heavily, but haven't pushed a city up to '4' yet (I keep restarting). Perhaps the late game/high tech structures could be given higher maintenance costs to compensate, or taxation needs to be put on a curve (so that a city with 1000 citizens won't produce tax revenue as efficiently as a city with 100 citizens).
The tax generation rate (currently .1) can always be lowered if that is considered too high, btw. This is what beta testers do, solicit opinions!