well, if you don't let it climb, then you are effectively doing nothing to balance sides...so basically outnumbering someone by 200 would have the same effect as outnumbering someone by 100. Doesn't really seem to make much sense if your goal is to level the playing field a bit. The idea of adding perks instead of disabling a plane might work, but only if it grew exponetially. 5-10 perks is nothing. If you had 1000, thats 100 lost planes, not exactly a motivator...add to that huge number advantage, it might actually be hard to lose a plane, thus making that form useless. Of course if you add higher eny, some maybe a spit16 is 200 perks, might be effective, but then again would probably have a very similar outcome as the current form of eny. Not to mention, you still might have to pay for planes that are free under when eny in effect. As to capping eny, you are basically asking to reduce the only measure AH has to encourage fair play.
I will never understand the argument that somehow the team with huge number advantage, is somehow the underdog in all this. There are plenty of planes that can get the job done, and you can still put many more of them up against the rest of the arena. Also you should have plenty of people to watch your back.