You're not going to experience any significant gains because at the end of the day not much hypertrophy is going on. That said, I do think it helps in a way. Walking on my heels for a week strengthened my tibialis (sp?) anterior muscle and I haven't had shin splints since.
Maybe not walking only on tip toes, but I would think "bouncing" on them every step would, sort of walk normally, then do the equivilant of a Calf extension at the end of the step if that makes sence, sorry I don't know how else to describe it. I do it very occasionally and although I can't comment that I have gained size, I am sure I would if I did it cosistantly because it really burns after a while
Hypothetically yes... I actually know a guy who was in one of those baby circular walker things as a kid when he was learning how to walk, and he was just a little to short, and ended up walking on his toes and has done so from that point on. He has pretty big calves, but theres no way to tell if it was just genetic or what.
The other guy is right, if your going to walk on ur toes all the time, your calve muscles will start to shorten resulting in inflexibility, I knew a guy who did that when he was younger and he had to get it corrected through surgery cause he wasn't able to go on his heels anymore.