Superfluous onEnterFrame?

I have a 3-tier navigation that uses onEnterFrame functions on each button mc on the 2nd and 3rd levels, to gotoAndPlay fade ins/outs if a “selectedVar” == 1 or 0. I have a couple of questions.

(1. If the parent mc of another mc is _visible set to 0, and the child mc has onEnterFrame stuff in it, will it still be calculated? will it waste CPU regardless?

(2. Is there an efficient way to handle this? I dont like using onEnterFrame for every mc, but i cant think of a better way to handle the thing…

The reason i use onEnterFrames is i dont want u to be able to drag ur mouse off the menu at any speed and have it stay up…so using a pissy little invisible button at the bottom to tell the menu to close is not gonna work…u drag ur mouse any faster than snail pace and it will stay up there