We have spent several vacations in the Smokies and I love it there. Like someone else said, it will be humid there but that is offset to me by overwhelmingly lush greenery, mountain streams, and green mountains. I think I like the mountains further north than Chattanooga myself. I would look further north in Tennessee or Kentucky.
Every time I have been up there I always start thinking about how I could make a living there. Of course, I do the same in lots of pretty places.
Someone mentioned the Northwest. I really love it up there too. That might be less culture shock for you guys but I think property will be a lot more expensive.
I expect where we retire to will be decided by where our children live. If I was going to move somewhere new I would do it as soon as possible so that we can develop close bonds and feel at home as we get older.