I went, too, and had a (laser)blast.
A couple years ago they did a similar thing to Plan 9 and I went. A lot more people turned up for Manos. I was surprised, because I'm unaware of any type of advertisement in the paper. While I was walking around the theater I did hear an ad for it over their radio, so maybe a lot of people found out that way.
I saw a story on Birdemic. The guy showed up at Sundance a couple years ago with a mini-van covered with hand drawn signs for the movie trying to promote it.
MST3K just put out Volume XXIV.