Just to clarify, the Princess Royal Walk (meet n greet) is the only thing you really wait for. Maybe the hair braiding and face painting which is done by cast members would have a wait, but not like the meet n greet. However, if you don't need one on one face time with an individual princess which would include an autograph and picture, you could easily participate in the other events and with some pre-planning, get a picture with your child turned around and the Princess telling the story in the background.
I have always been obsessive about the one on one thing, but I've learned to let it go. My daughter really never needed it as bad as I did. My favorite pic is when we were just walking through Frontierland and Pocohantas grabbed the kids hands and walked 20 ft or so. Luckily I was on hand to capture it, but it is so much more about the experience now. Goofy playing patty-cake as he goes along in the parade - just the best stuff there! I can only try to get as much as that captured so we can look back and reminisce. Pure joy!