If you like science and history, consider stopping at the Cosmosphere in Hutchinson, KS, on the way back. It's amazing. They have a great collection of rockets. German, US, and Soviet. They have the Apollo 13 Command Module.
On the way out, you'll be in BBQ heaven as you pass through Oklahoma. Consider Burn Co. or Albert G's in Tulsa. A local twist is slow smoked bologna. It's surprisingly good.
Zion National Park in Utah is on the way back. It's beautiful.
If you've never ridden out west in the summer; hydration is critical. Enjoy the trip.
When crossing Arizona there is a lot of Route 66 available. Williams Arizona was the last town bypassed by I-40 and very devoted to promoting itself as historic Route-66. From Ashfork Arizona to Kingman, Oatman and Gulf Shores is the longest surviving stretch of Route 66 remaining. Hackberry Store, Cool Springs Station and Oatman are all must see parts of this ride.