DO IT!! The party is fantastic. We are also doing the party on 11/1. It will be crowded but you can still enjoy everything and the lines for trick or treatin' go really quick. You get soooooooo much candy. The second parade is not as crowded as the first one. But get there early to see the headless horseman. So great! Some rides (like Peter Pan) have waits and I am sure the new Fantasyland attractions will be popular but we found most of the rides are not all that bad. It's also one of the only times you get to see all seven dwarfs together (found them last year by Splash Mountain). All the villians. Get fireworks show.
Can you tell we love it - this will be our 17th Halloween at WDW.