I think it is crucial to pick the right key for each song, not only for the instruments and voices that are to play it, but for the deeper resonances of nature that reside in each key.

Nice way of putting it, eta.
I agree, albeit from the perspective of one who has never really heard much of alternative tunings.

A friend has a Korg keyboard that you can easily set to a variety of tunings; quite interesting to hear the same music "filtered" in different ways. But we tend to agree that one tuning system is the best for any given tune, even if it's not the same for each.