I do this all the time, any computer game I play, I think out stuff to add to it, and sometimes come up with ideas for new ones (not just balance changes, but things like entirely new resources, units, advances, etc.). I'm wondering if anyone else does this to, partially out of curiosity, and partially because it seems very few people like to talk about this sort of thing (Even on internet places associated with computer games.), so if people it may give some ideas to talk about.
Lately I've been thinking how much fun it would be if EAGames would join up Battlefield 2142, Battlefield 2, Battlefield Vietnam (lame but part of their genre), and Battlefield 1942 into one big game with all the maps and the capability to mix and match but keep balance. For instance, have a map in which you can pit Battlefield 1942 forces against Battlefield 2142 units but keep firepower balance. You could limit the Battlefield 2142 side to one squad of 6 and let the 1942 side have three or four squads (or equiv number of soldiers) to keep the firepower balance. The 1942 side would have to have good squad management so that they could concentrate firepower to take down a 2142 squad member; The 2142 units would have to learn guerrilla tactics in order to evade the 1942 units better.
This would be in the style of Chuck Yeager's Air Combat, if you can remember that DOS based games from ages ago. You could fly simulated missions from WWII, the Korean War, or the Vietnam war in those era's airplanes or mix and match your own missions so that you could take a Messerschmidt up against an F4 Phantom. Each plane had it's own strength and weaknesses, so you had to adapt tactics that would work best against the enemy. For instance, a prop plane could turn on a dime, which an F4 or MIG couldn't, so you'd evade while they were attacking then turn at the last minute and punch them from behind with heavy caliber guns to damage them. You'd have a chance of taking them out after a couple of passes. If you were taking an F4 up against a prop, you couldn't use heat-seeking missiles, you'd have to use radar and guns, and make full throttle pass attacks against them to avoid being hit by their guns as you throttled by.
Another favorite idea I've had would be to combine the Battlefield 2/2142,Chuck Yeager's Air Combat genres with MechWarrior 2 and 3. This would give you the ability to be a soldier among whose missions could be to sneak into a clan camp and steal a mech.
How much fun could you have then??? Imagine a row of Summoners taking out a Titan with PPCs while P47D Thunderbolts try to stop them...

Something like a time-wars fest....