A piece of interesting info for y'all: the Tibetans would definitely agree with you that if you're spiritually advanced enough results like this happen as a byproduct. I suggest looking up the very recent (September 1998) case of Khenpo A-chos' rainbow body.
Although the sokushinbutsu discussion has got me wondering, would it be okay if I engaged in this kind of practices with a bodhicitta motivation when I'm old?