I am also interested in this question. We are used to WDW where people have opinions about where the best place to stand for parades are. Even in the Unofficial Guide for WDW it states where are the best places for the parades. But in the Unofficial Guide to DL it doesn't mention anything about this. Any help would be greatly appreciated!!
Celebrate is not really a parade (not a real parade, anyway). As the title suggests, it's a street party. When you enter the park, grab a map. It will show the 3 party zones. I prefer the zone over by IASW because there are fewer people.
When we were there, I picked up a chocolate covered mickey head pretzel from the big and lovely sweet shop on mainstreet, right when you walk in. I sat on the curn right in front and was right in between two parked floats and the characters and the dancers hung out there a lot. My kids got to play in the parade and we loved it.