I have a bias for CO and we are planning another trip to there is summer for the 10+th time BUT you've been to CO twice already so why a third time? I know that does not add up, but we've been to the NW 7+ times and will go back in a couple years and I assume you have not. I think the "Bad Lands" are well named and twice was enough for me as we are NOT desert people.
SO, my answer is "GO West young man, GO West".
Assuming a future trip to just OR & WA I would suggest going south from Glacier through the mountains of ID and then west through the middle of OR to the coast as posted in the last of the post above.
On that future trip I would go north from Seattle to Anacortes, WA and take the toad on the ferry to Victoria, CA and stay in a motel for a night or two.
