Hi Jonathan, have you been able to get some good detailed maps locally? If not, I suggest you purchase a Rand McNally road atlas from the RTA store via the link at the bottom of this page. You will see on those maps most of what there is to see along the way. Historical sites, natural wonders and even touristy attractions. You will also see just how many routes there are from which you can choose - from high speed interstates, to old US highways and back roads. Scenic routes are hilighted on all maps.
Those maps are not only invaluable during the planning stage, but are essential when on the road. Don't be tempted to rely solely on your electronics. Many have done so at their peril, some fatal. And if you bring the atlas home with you, you will have it for planning the next trip. It gets addictive you know!
As Dave said, it is hard to find anywhere 'least interesting'. Scenic routes and historical/natural attractions are everywhere, especially in the west. You're in for a great trip with hundred - maybe thousands - of attractions to choose from. It will certainly whet your appetite for a return trip.
If any of you are a member of your local automobile club, be sure to bring the membership with you. It will give you access to tourism information from AAA all over the country.
Enjpy the planning. Might see you on the road.
Lifey