Disneyland doesn't need NEW guests. It's filled to capacity all summer. You're right, guests who have never been before will never come for the first time just because of a new PeopleMover. But you underestimate the power of local and return guests. My mom would jump ten hurdles if it meant she could ride the PeopleMover or Adventure Thru Inner Space again. It would definitely turn up the attendance, with repeat guests and locals.
The concept of Tomorrow is dead to the world of today. Science went from being facinating to boring. Space Travel went from the final fronteir to passe. The world of tomorrow holds no wonder for today's people... sure, maybe new video games or mp3 players, but no one here has any real VISION past that. Walt didn't create a fascination with science in the 60's, he capitalized on it. Now that his dream in that sense is really dead, maybe Tomorrowland should be Vintage Nostalgialand.