If I don't play the second enhance, or it's canceled, does the multiple still copy the enhance?

My guess would be no since it's not a separate continuous ability.

Another question on the same card.. if you have 1 copy of say.. Megalomania, and your opponent also has 1 copy of the same card, is that another +1? Or does the one player need more than 1 copy?

The enhance will only carry over to the copies if it resolves. If negated, the enhance will not carry over.

I'd say if you have one Megalo and your opponent has one Megalo, that will count toward the enhance, since it says "in each player's staging area". if it was one or the other it would say more like "in a player's staging area."

I wouldn't have thought it would carry over if both players have one copy. Otherwise surely it would say something like "across all staging areas" rather than using a separating term like 'each'. You know, like in a way that says "we have one Megalomania each" rather than "we have 2 between us".

Honestly I strongly disagree with Tag on this, because of the wording "X equals the number of different foundations in each players staging area ." there is nothing that in those words means that if I have one battle disc system and Tag has a battle disc system we combine what is in play to figure it out the damage pump.