Wikipedia isn't the best source of information and I knew referencing it would ultimately probably not help.

Let me go back to the fundamental premise on "suspension of disbelief" as that concept was discussed in every literature class I took in college. "Suspension of disbelief" is not the same as "belief". It is when someone ignores the elements that are implausible or impossible for the sake of the story. The person still believes or doesn't believe in what they believed and didn't believe in before starting the story, but chooses to ignore or at least not dwell on those points.

This is easily applied to many of the points that you mentioned:

1. The Superman point. A person who believes that super beings could exist does not need to suspend disbelief regarding that because there is no underlying disbelief to begin with. However, he may still need to suspend disbelief that no one can identify Superman as soon as he puts on regular clothes and a pair of glasses to become Clark Kent because it still seems implausible. Another person, who doesn't believe that Superman could exist, would have to suspend disbelief on both points. Once again, the viewer (or reader, if we're talking the comic books) must simply ignore, overlook or not dwell on the implausible elements.

2. The horror movie point. Obviously, someone who suspends their disbelief isn't going to shout out "look out behind you!" (though stupid people tend to make stupid comments like that in theatres regardless). They just don't bother dwelling on the implausibility of a vampire/werewolf/monster/zombie attack, or an undead serial killer, or whatever it is, in order to vicariously feel the thrill of the scare that ensues. Someone who believes in ghosts won't have as much to ignore in a movie about a haunting as someone who doesn't, but the person who doesn't believe in them isn't required to automatically "believe".

3. The fairy tale point. Once again, we ignore the implausibility of animals talking, of magic carpets and wands and elves and fairies, of magical secret places on the other side of wardrobes or rabbit-holes to enjoy the story. We don't believe these things can exist, but pretend that they can exist to recreate the sense of wonder and mystery that accompanied a lot of things when we were little.

In every single one of these examples, there are points when the implausible elements can be pushed to such a level that the viewer or reader finds the suspension of disbelief impossible. This is the hallmark of bad cinema or literature because it breaks the story flow. It's not that the person "stopped believing" in something fake that they had "started to believe", but that the viewer or reader's attention is drawn consciously to a point that is so absurd it cannot be ignored. Remember what watching Highlander 2 was like - "Okay, this is a load of bullshit. Now they're all aliens, and there CAN be more than one?" Remember Phantom Menace - "We can measure the Force because it's really about little bacteria in you, the best pilot in the Galaxy at the age of six".