We went last October, and until a month before the trip, swore we weren't going to spend the extra $$ on MNSSHP tickets. But, after reading about the party and all the raves about it on the DIS, we decided to take the plunge.
It was great! DH and I enjoyed it as much or more than DD7 did. The parade was really good, and the special HalloWishes fireworks were amazing! The night we went was not crowded at all, and we walked right on Splash, Dumbo, Haunted Mansoin, Pirates of the Caribbean, Aladdin, Space Mtn, Buzz, and more. There were all kinds of characters around to get pics and autographs with, and the Trick-or-treating stations were giving out gobs of candy. There were DJs inTomorrowland and Fantasyland doing dance parties, and at the Castle, there were lots of Villians for a meet and greet. The atmosphere is just really cool- the decorations on Main St are awesome! Think about going- you should have a great time, even without kids. Many of the best costumes we saw were on adults (but you won't be out of place if you don't want to dress up- I wore a Halloween T, DH didn't dress up at all, and DD7 wore her Sleeping Beauty costume).
If you decide you still don't want to do MNSSHP, or want to do something else on Oct 31 itself, you do have a few options. As another poster said, the BW area has some activities- mstly for kids. DTD also has a bunch of activities, but I've heard it gets really, really crowded with locals. Fort Wilderness offers Haunted Hayrides during October, and Halloween themed movies at the nightly free screenings after the campfire. The storytelling and sing-along are also special, "scary"-themed during this time.