I actually love her voice. It's part of KM's and Janeway's special charm.
However, she might be a smoker, but that has nothing to do with her voice. If you find some of her earlier stuff, you'll discover that she sounds just about the same. I'm sure it has an effect, but not that great an effect.
About why I love Janeway...I've tried to explain that a million times, but nobody here seemed to listen so I gave up.
Listening is not the same as agreeing.
And anyway I personally love Janeway as a character. I just read Captain's Table: Fire Ship, in my opinion easily the best Janeway story in any medium and a personal favorite; she's the only character in it that we know, it's all and only about her.
She had a few writers that didn't seem to get her properly, but when written well even all those contradictions can come together into a uniquely compelling person.