Heck with Ben. I just want to meet Steve and Barney.
Brad
That the general consensus.

I'm confused on your timeframe. Are you taking three days up, five days in the Kalispell AO, and three days back? If you want to post an image of your proposed route, I could give you detour/alternate route suggestions. Otherwise, guessing where you might be going if you did the Utah/Idaho route:
Would you be entering Utah on 191 or 70? Either way, Moab and Green River are really cool. Outside of Moab is where we spread Monkeyleg's ashes. If your vehicle is not offroad capable, there's lots of rentals in Moab if you wanted to try a trail. Otherwise lots of "regular car" roads around Moab and the National Parks. Honestly, unless you really want to see it, Salt Lake City is just a big ginormous crowded city these days. I might suggest diverting through Heber City/Park City/Wanship/Coalville. Then hitting 15 again in Ogden, divert to Logan, then hit Idaho through Preston (Napoleon Dynamite! Rex Quan Do is still there).
From there you could hit 15 again in Pocatello and go through Idaho Falls, or, stick with me here - screw Idaho Falls and take 89 through Star Valley Ranch/Alpine/Swan Valley, then Rexburg up through Island Park, which is awesome and a gateway to West Yellowstone. Then hit Helena (super cool city) and then Flathead/ Kalispell as your base to Glacier. "Going to the Sun" Road, while crowded in Summer, is absolutely worth it.
For the way back, if you really want to see some pretty scenery and have the time, return on 93 through Idaho, hitting Salmon/Challis/Mackay, turn at Arco (don't forget to check out the sub and the atomics) through Idaho Falls and then whichever way you want to go to get home (I know nothing about Colorado).
The above sounds like a lot, but as point of reference, I once did Flathead/Going to the Sun/Helena in one not overly strenuous day.
If you take the East Idaho route, let me know ahead of time. I'd be up for dropping Steve at the dog hotel and spending a couple of days fishing the Henry's Fork (Island Park area) and could meet up with you for lunch or dinner somewhere in the vicinity between Idaho Falls and Wyoming.