Although I'm not a Tom Wait fan, I don't really have an issue with his voice (although I think to love Tom Waits you have to love his voice and not just find his voice tolerable) but more of the monotony of his songs.

Although Tom Waits did change his vocal style to John Mc trademark "cookie monster" voice did he actually wreck his voice where he physically can't sing in any other way or was that a conscious stylistic choice.

If it's the latter I won't really count it. I mean Bob Dylan couldn't sing like the way he did in the 60's as his physically incapable of singing that way not just because of stylistic choice.

That's my main thrust that they become a better vocalist due to physical impairment