If the Pixar Play Parade is playing, I consider that worth seeing--I can't say must see, because it's more fun and cute than impressive (to me, anyway), but if you like Pixar's stuff you should enjoy it quite a bit. (Just be careful your camera doesn't get wet!) The Disney website actually claims the characters from Ratatouille will be there but I think that's just a seasonal (summer?) thing.
If Celebrate! A Street Party is playing, I'd just look into it--I'm not really interested in characters dancing (or dancing with them) and the floats are very minimalist, so it's not really my style. It does feature some rare characters, though. I consider the Aladdin show (not a parade) a must-see.
Unfortunately, the Rivers of America will be drained during your visit, so Fantasmic! won't be able to run.