We have been to MNSSHP twice and I think it's really worth it. The first year we went our kids were younger ( 2 and just 5) and it was nice because we were able to go on alot of rides with no lines. The second time we went, our kids were 4 and 6 and it was awesome, we went on splash mountain 3x without exiting - love to tell people that! and everyone in our group went on BTMRR without me and the 4 year old. We went on line to see Brer Bear... well they were off the ride before we got our autograph. Space Mountain? 3 or 4 x in a row, Haunted Mansion? walk right in.. it is worth it not to wait on line. I don't go for the trick or treating. It's just a diversion!
The parade is wonderful too, I love the music they play when you are waiting, you can't get it out of your head.
The best part is, if you don't need to use a day of tickets if you have non-expiring passes or even a limited number of day. You can use the day as a pool day or shopping day or visit Fort Wilderness and then go to the MK when the party starts. At least that's how it worked for us last year. We even got in early!
Definately worth it in my opinion, especially eary on, I understand it books up in late October.