Well real expansion at the parks will drive up hotel occupancy rates, I think tdo has forgotten this.
Supposedly the armchair executive response to this is, "AK didn't significantly increase the amount of days people stayed here on vacation, so a 5th gate wouldn't impact it either therefore won't happen".
However, that's pretty short sighted, as it seems you get.
Look at Potter. I have no doubt people aren't probably spending a great deal more time at Universal then they did before (it's still just two parks), but we know that many more people are going there now, and they are spending a great deal of money on merchandise (apparently that's what's really raking in the bucks over there).
I think it's interesting how they are really going all out on advertising Star Tours. It's really a refurb - a very extensive refurb I am looking extremely forward to and going down just to see - but it's just the refurb of one ride. They really are marketing the hell out of the thing. It's a great thing, I think.
I can think of a few themes for a fifth park I'd love to see, and I truly believe with the right theme they really would increase attendance (AK is just difficult to market and the park - in spite of it's fans - is just not seen by the general public as a "full" park like the others; I truly think many people think of it as more like the waterparks in scope than a true "spend a whole day there" theme park, which it's operating hours supports).
All that said, right now, the current parks have plenty of space for expansion and the money should be spent on them, not infrastructure and everything else that goes with a whole park. That's why the Lucasland thing is so appealing, because they've got the space to do it already and MGM can so sorely use some more "for everyone" attractions (not just for kids, not just for thrill riders, for everyone in between).
We also have the possible resurgence of the Muppets on the horizon. Disney has finally stopped treating them like Disney characters and given over the reigns a bit - we have the first real Muppet movie since Henson died about ready to come out. If it's a big hit, then the real Muppets could be back in a very real way.
That's why after FLE, I really hope the next big development is with the studios, with a nice big Lucas area, and the ressurection of the Muppet Studio's idea (and, coincidentally, Muppet Studios is supposedly a big location in the upcoming film). There was a whole Muppet land planned (I read the stock holders report at the time - I was a kid and someone at Disney was nice enough to send it to me, it had everything from the original Toontown Spin and the ________ Tracy rides to the whole Muppet land idea).
So a new, large scope Star Wars ride. Maybe Indy.
A Cantina-themed restaurant. Add a large-scale Muppets dark-ride (the Muppet Great Movie Ride still seems like a great idea), convert the Italian restaurant into the original Muppets idea...and bam, you've got a whole new reason for people to come to WDW, and two already popular and promotable brands to attach it to in advertising.
Oh, a boy can dream, can't he?