They HAD to realize that this year would be a 'let-down' after the 'end' of last years 18 month Millenium Celebration (which was extremely successful), because after it was over it left a pretty big void (Millenium Village gone along with some of the 'spirit' of the new Millenium). Now since Disney didn't plan anything for this void, they basically should have planned on the let-down. In fact their promotion "asked" for it...urging you to visit during the Millenium celebration, so it you couldn't visit (or visit again) until a month after it was over, why go (you missed it, dummy), it's like getting to a movie late and missing most of it. And then there were those who planned a vacation for 2001, and pushed it up to 2000 to catch the MC.
Who ever though of the current cycle of closed ended 'celebration' promotions is a narrow minded idiot. Instead they should promote the following new 'stuff' in celebration of this-and-that. 'Stuff' that doesn't go away, but 'stuff' that gives you a good excuse to visit.
Jan 1, 2001 should have offered something new to fill the void left when the MC ended.
As far as increasing attendance beyond the general fan base...
When AK opened, attendance increased slightly overall at WDW, and AK attendance was great, but most of it was pulled from the other parks, not additional (spanking new) visitors.
The fact is, Disney fans like us return to WDW over and over again because of what it 'has' and 'is' not because it added a new E attraction. Yes, we like to see new stuff and a degree of change (for the better and not at the expense of our old favorites), but we go to see Mickey, ride the classics, enjoy the shows, and just 'be there'. Sure, a new E attraction (or celebration) can be a good 'excuse' to plan a vacation around, but nobody goes for the 1 new attraction alone. When AK opened it was great for us, lots more to do, but there was no big 'signature' attractions to pull in new people, just existing WDW fans coming back again.
Believe it or not, there are a lot of people who resist going to WDW, even if they can afford it...sort of a stubborn resistance against being brainwashed by or giving their money to the Mouse (my x-in-laws are like that...they went once way back when, so why go again?), or a simple adversion to happiness (some people just like to be miserable...like my mom). The only way to get these people to go is to make a specticle of yourself by opening an insane new ride...a ride that makes the kids beg the anti-Disney parents to go or is just so big they want to go themselves to see what the big deal is. Universal did it with IOA (the x-in-laws went for a 1 day trip, and will probably never return), Sea World did it with Atlantis and Kracken, Busch Gardens with several new big rides in the last 5 years. WDW has only added Test Track and Rock and Roller Coaster, neither of which are big splashy attractions due to their ho-hum themes (driving a car and listening to Aerosmith, ZZZZZZZZZZZZZZz), neither of which would appeal much to stubborn old Dad.
As far as I'm concerned, they've been adding a lot of Disney touches since my daughter was born, making every trip more magical and special than the last and gave us a bevy of new stuff to enjoy (from AK and character meals, to Fantasmic), but from a promotional perspective, nothing to convince a stubborn old Dad to go for the first time.
Since they can't instantly add a new E attraction, they need a gimmick, like replace the wand in Mickey's hand with the WORLDS LARGEST UNITED STATES FLAG waving proudly over Spaceship Earth.