HiTech and Pyro hit it on the head when they said that the pilots want to fight pilots, army guys want to fight army guys, and navy captains want to fight navy captains. The truth is the different gameplay ideas don't mix well. Everyone always uses what is most effective. If ground vehicles become more effective than planes, that is exactly how the game will be played ALL THE TIME. We can't let that happen. Nobody should be better than the rest all the time.
That doesn't mean the game cannot be setup that SOME targets are easier to kill and capture with vehicles, but others are better suited to airpower.
I think army base versus army base should be setup that the army vehicles can do alot more damage quicker than air attacks. Things like well entrenched AA guns that take a hell of a lot of bombs to kill, yet are so dug in that they cannot fire at tanks and such. Trenches with small arms fire out of them killing any infantry near them, which are damn near impossible to kill with bombs alone. You have to close assault them with tanks. Rings of barbed wire fences that can only be breached by driving a tank over them.
Conversly, airbases should be hard to attack with vehicles. One thing that easly can do that is anti-tank minefields ringing the airbases. Strategic targets obvioulsy are easier to attack thru airpower by geography. No change there.
The key to more ground combat is to give it it's own spot on the map to have the fights, but not the whole map.
