Suggestion - "stacking" spending orders
(Ordering things before you have the money for them)
Several times towards the end of a game I have found myself generating sufficient resources that when I was actively managing a battle I would have stockpiled lots by the end of it, even when I had spent down to zero before the battle started.
Why not allow you to "stack" orders even when you don't have the resources for them and only have them execute when there are sufficient resources to build things? (On a "first in, first out" basis). Before a battle starts I could start some expensive techs or request the building of reinforcements so that while I was fighting my empire would be automatically sending me reinforcements as soon as it had enough cash to do so.
I'm not suggesting that you should be able to borrow resources and build things before you generate the resources yourself (though a sufficiently expensive 'loans' system might be interesting)