This will be our 4th year. We LOVE
MNSSHP. We dress in theme as a family. We have gone as POTC (2 different years) and Peterpan. This year we have a large group (about 12) going so needed a broader theme so we are going as 1920's gangsters/molls/flappers. CAN'T wait!!!! A lot of people dress up, most of the kids dress up some adults don't ( I saw a toddler snow white and her dad as prince charming- I was in awe- it was so cute!)
It's hard to tell everything w/ out specific questions. But one thing I will say is don't plan on it being a park day before hand even my 7 yo(he's 9 now) had a hard time keeping up toward the end of the night and if you spend the money and the time plus costumes etc. it's a bit irritating to hear "can we go yet?"
Also, if you are a pin trader/collector every night there is a different limited edition pin for the event. I always try to go on a night when it's Tink.
There are lots of locations for trick or treating and a couple "treat trail's" on the trails you can hit several locations and see lots of characters , the alice and wonderland one is my fave. The red queen is all mean and the mad hatter makes jokes w/ the kids or comments on their costumes and what not. It's one of the rare WDW times when you get to see characters w/ a little freedom not just standing in line for a photo op. They're not just wandering around the park but they walk around the treat trails and some other locations. Be sure to hit one of the trails at the latest possible time, they will usually (some CM's are cooler than others and in my opionion you want to steer clear of old ladies

) unload candy on you at the end of the night.
EVERYBODY gets to trick or treat so make sure you have bags for adults and babies too and you will score BIG! Also last year a lot of ppl were up in arms about the raisins they were handing out and you can pretty much say-Hey keep the raisins and they will give you candy. I went behind all of them (I have had a 1 yo w/ me) and said I'll take the raisins and my daughter had on the go handy little packs of raisins for MONTHS!!! Clever snack hording on my part I think.
Good luck making your decision. I hope if you go you have a wonderful time. Feel free to PM me w/ any questions.
...t.