We attended our first MNSSHP last Friday, and thought it was excellent. We arrived at 4:30, and went right in. We were able to get in about 5 rides before 7pm. As it got closer to 6pm, the park emptied out, and we were able to walk on several rides in Fantasyland. Splash Mountain had a 25 minute wait around 5pm, but we were told to come back after 7 and it would be much better. This turned out to be very true, and we walked on later. Overall, we waited no longer than 10 minutes for any ride, and were able to ride several rides multiple times. Space Mountain, Splash Mountain, Big Thunder Mountain,Haunted Mansion, Pirates, Jungle Cruise, Snow White, Carousel, Winnie the Pooh were all walk ons. After the first parade Big Thunder Mountain did have a line, however we were able to walk on 2 times in a row during the parade. The only real lines where for the characters. Candy and picture lines took less than a minute. We found it not to be overly crowded, and was a wonderful time. According to a CM 19,000 can come to a MNSSHP at sell out level. We were also told 33,000 were in the park the day of the 8th. Several CM's told us how much shorter rides where that night than during the day. I wouldn't worry at all about attending a sold out party, they are easy to get around and a ton of fun. 

and thanks for the wonderful review. It sounds like you had a great time. It's amazing how well Disney handles big crowds, isn't it? Did you all dress up? We're going to the party on the 28th, and I can't wait. My granddaughter is going as Lilo; the rest of us are her "cousins."
The 8th had Cindy's coach out in Ariel's Grotto, but it wasn't there on the 3rd which was a treat. We also saw Snow White & the 7 dwarfs in Fantasyland on the 8th, but not on the 3rd.
We had already done all the rides we wanted in there, so we just sat around waiting. The lines for those rides were really long too.