But the really bad thing about being rich is that you're wasting your money.
Not entirely true. In fact, in most cases i'd say entirely untrue. If your faction is in control of a large amount of provinces, then there is no reason why you shouldn't be filthy rich. Even with a steady recruitment process in place and all towns expanding you should still be raking in the profits. It is actually quite difficult to spend , unless of course your the mass producer, you know the type, the ones who just build armies and fling them at any and all opponents(not saying theres anything wrong with this), with the "screw the casualties, just smother the bastards with numbers" attitude.
Of course, bribery becomes quite the bottomless pit.
All in all though, a little strategy will go a long way. With all your provinces building and recruiting, there is no reason why you should not be rolling in the green.