[Commander G]

I agree with the others who state that fighters should have a maintanence cost. If you look at current day fighter planes, they require constant maintanence and the pilots neet constant practice, both of which are considerable expenses for their militaries.

Having units free of maintenance encourges players to build as many as they can until they approach their limit. Then they have to start dismantling them to replace them with better models. As players learn how to optimize the game, this will become a big advantage for micromanagement players (those without families or other persuits in life).

How about facilities? They are absolotely free of maintainace. You can build a research lab and never have to pay another resource to keep it going. If they were to add maintainace for these, they would have to adjust the numbers a bit to keep expensive facilities like Monoliths cost effective.