This is the route we took home from the Balloon Festival. We left Sante Fe and went directly to Denver so I can't speak about the first part of your trip. After Denver, which was a bear to drive through by the way, it was a very easy drive. The KOA in Billings is the first one of the chain and is very nice if you happen to be there when you need a place to stay.
The hill as you approach Butte is a long grade but the remaining passes in Montana are not so bad. You will see lots of beautiful country. Watch for all the antelope in Wyoming.
Spokane isn't so bad either. Hmmm, we don't have any BBQ to speak of although there are some new wanna be places popping up. Our politics are similar to Texas, unless you are from Austin, and you will have to put up with the Mariners (or not). We have 4 seasons and rain is not a big problem. When it does rain, it isn't during a hurricane or tornado. You can entertain outside without getting eaten by bugs, you can sleep in the ground and not worry about chiggers and if that volcano didn't blow, this place would be close to perfect.
OH, and Washington has it all. We have deserts, rain forests, sandy ocean beaches (cold water though), Puget Sound tide pools, the densely forested coastal range, arid high mountain forests of central and eastern Washington, farm land for miles, wheat fields and tons of wineries. Yeah, not a bad place and it is not all privately owned either. You can still camp for free many places if you know where to look.