"I Horror Surrealism?" is a pretty surreal thread title.
Funny about the Boogeyman not being there on the ground (after he was shot and fell out the window). I never got that he "disappeared", I just assumed he got up and moved, maybe going back to the front door of the house. That would have been following the trend of events up to that point.
If Carpenter really wanted to make him disappear, he should have either shown him visually fade out, or leave the clothes empty, or the best solution would be have the Dr go to the window and see him laying there on the ground, then turn to Laurie for just a slip second and then look back at Micheal, and he'd be gone.
Personally, I think there's a place for surreal horror films, Nightmare on Elm is a classic case. In general, I prefer horror films be very sparing in total surreal. Films like The Beyond aren't my cup of tea. I think a film has to establish the real for people to grab a hold of, especially in horror, where sometimes it's real harm that we fear, but if it's all a dream, there's nothing to fear. Plus, a strong reality will then give the surreal some real contrast.