Might I suggest staying north in Wyoming rather than turning south after Devils Tower and heading twords Casper? You can take I 90 to Buffalo and Highway 16 or further on 90 to Sheridan to Highway 14 and take a nice scenic trip through the Big Horns. There are other options near Sheridan for some light dirt road travel that round abouts back to Highway 14.
Then take Highway 789 on the other side of the Big Horns down to Thermopolis, home of one of the largest natural hot springs. Pool and water slide available as well. Next is Northwest on Highway 120 Which will lead you to Meeteesee. From Meeteesee you can visit the Old Kirwin mine, easily driven by a stock TB. I made the trip there last year before installing my lift. Also you can visit Jack Creek camp ground and drive Phelps Mountain road, accessable by 4X4 only, but this is just the initial portion of the road, once on top it's fairly smooth and provides various view of Shoshone National Forest.
http://www.fs.usda.gov/Internet/FSE_DOCUMENTS/fsbdev7_004815.pdfBack out to Meeteese, then North on Highway 120 again to Cody Wyoming. There is plenty to do with the Buffalo Bill Museum and a nice lead into Yellowstone National Park.
Just a few options available rather than a most boring drive from Casper to Dubois as it appears on your map that was your intended route of travel. Not that the drive from Dubois up through the Teton National Forest isn't wonderful, just that up until that point it's quite boring.
On your Montana route it appears you intend to go from Helena through to Choteau on I15/Highway 287 on your way north to Glacier? Rather than go that route north, which will be drab once again, might I suggest either taking Highway 12 out of Helena to Avon, then North on Highway 141 to meet up with Highway 200. Or at Wolfcreek take Highway 434 and meet up with Highway 200 and head through Lincoln, home of the Unibomber. Not much in Lincoln, though there are many roads to travel. Main point from here to to meet up with Highway 83 and head north through Flathead National Forest, the drive is amazing, campsights and the lakes are certainly to be seen. From there you can hit Glacier and then backtrack slightly to Kalispell and continue your trip as noted.
Just a few additonal ideas for you to think about.