I agree that it certainly is fun to think about and discuss!
I'm not quite sure what the bowling ball on a trampoline analogy has to do with the theory of parallel dimensions, or how the lack of a universal understanding of the nature and function of gravity would prove that there are multiple planes of existence. Saying that something "makes sense" and proving that it exists are two distinctly different things. In fact, you make this point yourself in describing the emotional response of individuals experiencing what they believe to be paranormal phenomena. The concession that responses or experiences of such phenomena tend to be more emotional than tangible strongly indicates that the phenomena are the result of things happening in the brain of the experiencer, rather than an external event. You say our minds can't comprehend another dimension, but I would argue that "another dimension" is merely a creation of our minds, designed to explain things happening in our own minds which our own minds can't comprehend.
Bigfoot, the Loch Ness monster, and alien life forms should not, in my opinion, be lumped together with ghosts, because they are things that, if they exist, are tangible and exist in the natural world, but are currently undiscovered. Ghosts, on the other hand, are a manifestation of all the traits of self or personhood, but without the physical apparatus (a brain) to create and connect them. If Bigfoot exists, that doesn't fundamentally change our understanding of life or biology; it just means an undiscovered species has been found. If ghosts exist, on the other hand, it means that the mind is more than a function of the brain, that life is more than the chemical reactions of the body, and that personhood is more than who we think we are. It has more than scientific ramifications; it has philosophical and psychological ones as well. It is also far more difficult to prove than the existence of a cryptozoological creature.