I haven't played a whole heap of FoTS yet (only got it yesterday) but from what I've seen there is no agent or building type that raises tax rate or reduces administration costs in a given province? if so then specialisation province is no longer a priority economically and xxxx investment in province A will yield the same net benefit as xxxx investment in province B. The key drivers will be exploiting privince resources for more effecient troop recruitment, and managing happiness.

But like I say I could be wrong!