It might not provide a lot of knowledge to the subject who practices mysticism. It does provide the best experience in his or her life.

For the time being, this might not provide a lot of value in the grand scheme of things. However, as we advance into posthumanisty, we do want to explore the state-space of possible conscious experiences in a systematic way so we can design ourselves in such a way that we inhabit the best regions of conscious experience. Mysticistical practice, therefore, has a tremendous long term potentintial; having practicioners and scientists interested is crucial if we are indeed to find out more about these states of consciousness.

I think, after all, there is a very pertinent parallel in the community of lesswrong: it is called fun theory. The fact that mystical experiences can be so outsandingly great and sublime beyond words is a very strong indicator that we will never run out of fun.