Think about light movement, time of day and driving endurance. In the mornings the light will be genrally behind you and ease driving, while in the afternoon it will be in your face. Your family also is likely to rebel if driving legs stretch too long. In addition to finding must-see locations I'd develop a strategy for your trip which combines the best elements of all. I.e., do most of your driving in the mornings to reach afternoon destinations for dedicated family fun. Evenings and early mornings will be your photo ops. If driving East, reverse the schedule with mornings for fun and afternoons for driving, and again reserving evenings and early mornings for photography.
I'm not sure about further east, but commencing at around Denver, Hiway 70 presents an excellent mix of destinations all across Colorado and into Utah including Rocky Mountain NP and the Colorado National Monument, with lots of lesser known destinations between. You cold also veer south an hour for Arches, Deadhorse Point and Canyonlands. You could continue south from there and hit the destinations listed below for your return or continue on 70. Hwy 70 terminates at US 15, but swing south about 30 miles and resume your westward movement on Hiway 50 through Nevada, into California via Lake Tahoe and Sacremento. It's relatively short hop south from there to Yosemite. On the eastern leg I'd veer further south and take in Death Valley, Red Rock, Las Vegas, Valley of Fire, North Rim of the Grand Canyon, Hoover Dam, Zion, Bryce, Escalante, Natural Bridges, Lake Powell, Canyonlands and Arches. If you continue on that general southern crossing, you could also conceive a route through Great Sand Dunes and other lesser known spots.
I make annual or twice-annual swings through the area I describe, and my biggest problem is time. There's so much available that you have to carefully balance you available time with carefully selected stops.