I'll be there -- though I probably won't dress in costume. One year I actually planned to go as a Goofy runner -- complete with racing bib and medal, but then spent all day in the parks and never got back to the room to change into my "costume."
My favorite part of the MNSSHP is getting photos with my favorite characters in costume -- like I have one of me and Cowboy Goofy, and me and Scarecrow Mickey, and me and some-sort-of-royalty Donald. I love that.

You can also get your picture made in front of Cinderella's carriage, in front of some scary backdrop at the Haunted Mansion, etc. etc.
I never do the trick or treat stuff, but I love the special fireworks and the special villians parade. I have a great time just wandering through it all. It's just good simple fun.