It's not just the distance to Mars, its the gravity well we would have to descend into to get there (and escape from to leave there).
I suspect that once we have the technology to live in space for the time it takes to travel to other planets, we will have no reason at all to plant ourselves on another one.
Yeah, that's the idea of space settlements. Check out this link: http://settlement.arc.nasa.gov/
But I don't know, I wonder how well permanently floating through space would affect human psychology. I realize that the whole point is that we could build them however we want, but you have to wonder if it won't be hard for humanity as a species to move to a permanently enclosed space.
Ask anybody born and raised in New York City. Homo Urbanus loves that enclosed life style.
Me personally, as an instance of Homo Ruralus, I would have a harder time with it.
But it's what you know, and Homo Spaceus will probably love it. :)