But not as scary as you think.
I'm sure a combination of The Phantom of the Paradise and Hell House double bill sounded great... but there's something incongruous about kitsh and failed evil that doesn't inspire.
Hell House is based on the great book by Richard Matheson made into a good movie. Just good. Not the soul rending nightmare the book is. It's a better book than Shirley Jackson's Haunting of Hill House, but the movie made from that is better than the movie of Hell House. That said, watching the Hell House movie is still a good way to spend time.
There's a rumor going about that it's going to be remade. This is not a bad thing (the way the Haunting remake turned out to be), but if they do a remake, call it Belasco House. Such a title will allow for a bit of updating and a full force recreation of some of the book's more intense aspects on screen.

San Diego Union A16. Halloween 1975.
The Clairemont was a single screen that was doubled before being turned in "retail space."  The building still stands. The Balboa is being renovated- office and theater use, hopefully they'll show movies at some point. The Vogue just closed in Summer 2006- killing the last "cheap house" movie theater in the county.
Sadly, the Campus, Harbor, and Pacific Drive-ins are no more.