I really can't see any benefit to such an extended stay besides saving on airfare.
Its hard to explain I guess, and if you've never done such a long vacation at Disney it might be difficult to picture - but you truely feel more immersed in the magic, not less. You won't have that "ok we'll be packaging up again in 5 days" lurking in the back of your mind. You don't end up with that "need to take a vacation after my Disney vacation feeling" - you can actually relax, take your time and enjoy all the little things the resorts and parks have to offer. It is a very different vacation, but a more relaxed one where you can take everything in and really get in to it. Having done both shorter and very long vacations, given the choice, I would now always go for 1 long vacation (3 weeks), rather than 2-3 smaller ones throughout the year. Everyone's different though - but if you haven't tried a long vacation at Disney, give it a go - you might be surprised
