DCA has the kid-centric trick or treating party, so why not have a just slightly more dark event after hours for Disneyland during October?
My basic idea is the whole thing would be anchored more or less around Haunted Mansion, that being the icon attraction for the event...and structure it so say the open areas would be Main Street, NoS, Adventureland, Frontierland and the Big Thunder Trail, the Fantasyland courtyard, and Tomorrowland just to front of Matterhorn/Alice. Closed off areas would be the back portion of Fantasyland and Toontown for the event only. Some of the park would already have decor, Frontierland and Main Street, and all of the park would be lit with purples and oranges, eerie colors, and occasionally have these lights dim and simulated thunder/lightning and fog effects.
Roaming the event would be large amounts of Mansion themed performers, like the Caretaker, cemetary ghosts, ballroom dancers, a eerie old style bride with the glowing heart, and butlers and maids as well, with the three Hitchhiking Ghosts lingering outside the Mansion for photos with guests. New Orleans square and the main portion of Frontierland could recieve more decorations, hay bales, scarecrows and jack-o-lanterns for Frontierland, and mardi-gras style voodoo accourtrements for NoS, on the back streets, bones and black wreaths and such, more nautical styled things like skeletons and chests of treasure around Pirates, with the Bootstrappers playing a selection of spooky sea-chantey type songs, along with Grim Grinning Ghosts and some classic Disney music, an arrangement of the Skeleton Dance perhaps.
During the event, select attractions would be open only that fit the slightly darker Mansion theme...Pirates, Mansion, Indianna Jones, Matterhorn, Snow White, Space Mountain, Mr. Toad, and perhaps Jungle Cruise with a special more ghostly skipper and eerie nighttime tour, ghost stories on the Mark Twain, and station some western or pirate themed performers on TSI/Pirate's Lair, and have that open for the event.
A special fireworks should would be nice, again themed to Mansion/Villians and such, and a parade similar to the Disneyworld Boo To You Halloween one, which would be the only place save for Main Street where Mickey and the gang would appear in their Halloween costumes.
It is a touch bit darker I know than the current offerings, but I am not thinking at all of Knott's Scary Farm level scares here...the roving ghost performers would all be more slightly funny and interactive rather than scary.