If Disney decided to do a few Halloween nights at DHS, I think they should avoid Haunted House stuff. Uni has that covered and does it better than Disney ever would. No party at DHS could compete with HHN. Doing HHN Lite wouldn't cut it...neither would a slightly edgier MNSSHP. We have those events. DHS needs to be unique and do its own Disney thing.
They should stick to Villains, fireworks, Meet & Greets, music and shows. They have that BatB theater and the stage by the hat. They could do some awesome stuff.
I'd love to see a smallish Villain parade (or show) with that Twisted Sister "We're Not Gonna Take It" song. I'm a very limited demographic, though.
Something along those lines. Villains. Rock.
(And not the dreary, "Ooooh, the world sucks and I'm so cool and jaded because I hate everything" kind of rock. Upbeat. Pounding. Fun.)
Honestly, I see no reason it has to be Halloween themed at all. Any Friday the 13th is a fine excuse, if they need an excuse. Villain Fest would be great any time, though. IMO.
They could also just bring the villains out on a regular basis and make the park experience that much better. That's like heresy amongst Disney management, though!