Exactly. The power of suggestion really can elaborate upon the optical illusions in such "mystery spot" style attractions, producing a pretty amazing experience.Knotts Berry Farm used to have one of those "haunted shacks" (don't know if they still do), and it was one of my favorites.
It takes a combination of things for this one to work.
As you mentioned, forced perspective is one.
Another is the surroundings - even though all these rooms are built on a hill, the walls and doorways are built at a right angle to the slope of the hill, not to gravity...and there is never a window or doorway that allows a view to any horizon. Since the eyes can't find any outside benchmarks for what is "level", they begin to take over from the inner ear, and perceive the room to be "normal" (well, normal"er" than it really is) - this is why things appear to move uphill, and someone can sit in a chair that's just resting on a shelf on the wall, without toppling forward. Even though the pitch of the floor may be significant, the brain begins to believe it's just a slight angle, so these "miracles" become believable.
Finally, the power of suggestion. You have to keep up about the "mystery" and "anti-gravity waves" and "haunted forces" that power the place. This, along with the un-noticed confusion people have from the angle, and lack of outside reference, will give the mind it's "answers", when it can't make sense of things.