I agree with the other posters...if a particular view is important, book it. You don't want to spend even a moment of your precious vacation time disappointed that you didn't get the upgrade you had counted on.

Upgrades really seem to be random...you can always fax ahead and always ask at check-in, but you just never know.
That being said, let me share two personal experiences with Disney Resort views. Two years ago we booked a garden view at the Grand Floridian because the rate was too good to pass up. We determined to enjoy our room no matter the view because, afterall, we were at Disney, and what's a view, any way?! Upon arrival, we were informed that we had received a complimentary upgrade to lagoon view, which, of course, we were thrilled with. It set the tone for a really special week at Disney! We love to feel like we're getting a "deal", we loved watching the electrical water pageant from our balcony and we loved hearing the haunted mansion, music and train in our room. We went home very happy.
Last year, we booked at the Wilderness Lodge, and because we were hooked, we booked a water view room (the most expensive category, and we were even told by CRO we'd have a view of the geyser...yippee!) We reasoned the extra money would be worth it because we had so enjoyed the view the year before and we didn't want to risk looking at nothing all week. Well, when we anxiously entered our room to check out the view, we were very disappointed. Our only view was of scaffolding and workmen, who remained outside our window daily for the duration of our trip. Whenever we were in our room, we had to keep the curtains closed...the rooms are small and dark as it is, so it was really a bummer.

It was terrible to pay for more and receive less...(the resort was sold-out so the problem was never resolved...technically, we were in a water view room...we just couldn't see any water!)
Anyway, sorry to be so long-winded...lesson learned for us...we'd rather get a great deal, and IF an upgrade MAGICALLY appears, wonderful...if not, we're happy with the great deal and hey, we're there for the parks anyway. You're the only one who can determine whether the view is the make it/break it for your vacation! Good luck and have a great trip!
P.S. We live here now, so no more view problems for us. We had breakfast at the AKL a few weeks ago, and I agree with the poster that said the view choice is important there. The animals are amazing and I know I would love to sit on my balcony and watch them. The resort is beautiful (and breakfast at Boma's is GREAT.) Enjoy!