Hmm, i think they do need the mountain.
Test Track has done a great job of showing people who wouldn't usually come what a great park Epcot is. I believe that Mission:Space will also do the same. Now come on, don't get me wrong, Maelstrom and American Adventure are great, (Maelstrom would be even better with small changes) but a Mountain is really needed to add to the Adventure and excitement of the World Showcase, wherever it be, it needs to come. Disney must know this.
I mean, take for example myself, I go to Epcot, and I see no reason to wander to the left of USA, sure there're movies over there, but nothing that sounds cool to me. A mountain, however, on the righthand side of the World Showcase, WOW, cool, I walk over to that side of the Park "hey, why don't we grab a fastpass for the MAtterhorn and head over to see O Canada. Wow, look at this, I feel like I'm really here" etc... Any E-Ticket on that side of the park is a good idea, a great idea.