The other place I'd consider is the Rockies. But, loneaspen, what is your opinion of the growth there? Seems like everyone and their brother want to move there. That would be my concern, especially with impending water issues.
Since leaving Colorado in 2007 and moving to Silicon Valley, I've only been back a couple times for short vacations.
However, based on everything I'm reading, including watching how housing costs are rising in the Denver area, I think your concern is valid, and it concerns me, too.
When I lived in the Denver in the mid 90's, I remember it being typical big-city-ish, but the crowds and roadways weren't crushing. After living here in Silicon Valley for a number of years and experiencing what seems to be a resurgence in the economy (at least for tech workers in the Valley) and skyrocketing housing costs, if I assume that the similar rising housing costs in Denver can be correlated, then that tells me the Denver area might also be getting similarly overcrowded, with crushing commutes.
I don't know about the Evergreen or Genesee areas, though. Something tells me the foothills areas will always maintain a more sparse population because of housing density, and a lot of people won't put up with the weather or the commute.
If I were to live in Denver metro area (including Castle Rock, Parker, etc) the crowds would definitely concern me. With Evergreen and Genesee, it would be water and wildfires. It's scary to me that there will not be enough water in the Denver area to support that many people if the drought continues, which I think it will. I could definitely see people in the foothills (especially those on wells) having to install cisterns and get water trucked in, which I think would kill resale values for foothills properties.
And the wildfire concern is enough for me now that I probably would no longer look for a house "in the woods" and surrounded by trees, as I've had in the past. I'd probably look for something much more in an open area, even though I'd miss the privacy.
But...even with these concerns, I still see myself moving back there. There's a big part of my soul I feel I left behind in the Rockies when I left (particularly Colorado) and I've got to get back at least for a few years, and enjoy the things I remember so fondly from when I lived there before.
EDIT: Regarding other parts of the Rockies, I've only visited Wyoming and Montana, and my initial thoughts would be similar to the Evergreen and Genesee areas of Denver...that those areas (like Bozeman, Billings, Cody, etc) won't be growing at a rapid pace. I could be wrong, however...maybe places like Billings are growing a lot. But I would expect there are always places out the outskirts to live, that they still won't be that crowded. Although, if I ever moved to a smaller town like a Billings, it would only be for a couple years, because there are things I would miss about being near a larger city like Denver.
