Dr John Campbell (in talking about psilocybin treatment of depression which he supports research on) doesn't think it's the "mystical experience" that fixes depression, thinks sub-psychoactive doses might work. And certainly it hasn't been proven that the mystical experience is necessary for the effect. But if he had ever done mushrooms himself I think he would have a different opinion. He admits that depression comes from a feeling of hopelessness. Why can't he see that a mystical awakening would logically dissapate feelings of hopelessness? Not proven, but based on my personal experience I think it is very likely that the mystical experience is the core reason for the cure.
Discussion
Also, the feeling of "no hope" that leads to suicide is not counteracted by a belief that there "is always hope". Trying to give people hope doesn't work. Their brains function well enough to know with some certaintly that whatever they desperately hope for can never be.
Rather, the cure to depression is the realization that hope is unnecessary because all situations are tolerable and magical and interesting regardless of how bad they are labelled to be.
In one word, acceptance, right? What about self-knowledge?
Also, it would be interesting to investigate what causes the lack of hope in the first place. If we find out, maybe we could be more proactive.
On a related note, I recently read that the common theory of "chemical imbalance" in the brain was disproven. Also, according to an article headline I have seen, physical exercise is a better cure for depression than the usual drugs.