OK - so I have been attending a Zen center and doing koans and zazen (sitting meditation) there for the past 6 months or so. I definitely like the calming and "centering" of awareness that I get from meditation of various types. I attach no "supernatural" attributes to this. I do think that our minds are often very inefficient and bound up in unnecessary chaos which awareness can help "treat".
On the other hand even in Zen, which is supposed to be sort of spartan and free of superstition, the "Dharma talks" use a lot of mystical sounding mumbo jumbo - not always, just sometimes. On the other hand, with a little mental effort on part of the listener, terms can be substituted to make the talks palatable to reasoning minds. "We are the Buddha" - can be interpreted in Carl Sagan's terms as "we are made of star stuff", "we have the cosmos within us", "we are the cosmos aware of itself" etc. All very true, all very "Zen".
So I am currently trying to figure out how much of this Zen is free from superstition and therapeutically valuable, versus just another religion with an Asian flair.