What makes haunted houses less scary? The anticipation. You know something creepy is around every corner. That takes the level of fear down a few notches. Same as with a horror movie.
So, what if a haunted house slipped a few cast members in line dressed as regular people. They’d talk to you and act scared and earn your trust. Then they’d go with you through a few areas and in one area “accidentally” get an arm cut off by a chainsaw or stabbed by a stumbling maniac. Wouldn’t that destroy your level of anticipation? Surely. Sometimes the most obvious things can change the game.