Hello and welcome back to RTA !
It would help a lot if you were to elaborate a little on how much time you would like to spend on this trip. Heading down towards the Grand canyon North rim would add about 600 miles to your trip as opposed to heading to I70 via US6/89 and at least 2 days of driving with a quick 'peak'. As well as the North rim of the Grand canyon there would be the NP's of Zion and Bryce canyon, and possibly Capitol Reef if you had the time to take Utah scenic 12 through Escalante. To head down to the GC and enjoy these other natural wonders could easily take up a week of your time, but at least 3 days I would recommend and that's if doesn't leave you having to race by all the other natural wonders.Time will be of the essence (looking to see the highlights, but not spend multiple days in any one location).
If you went to GC or not your next 'major' attraction would be Arches and/or Canyonlands near Moab UT. After which there are the like of the Colorado National Monument, [near Fruita] the Hot pools at Glenwood Hot Springs and at Idaho Springs. Prior to Idaho Springs [and by-passing it altogether] you could take a trip through RMNP on the spectacular Trail Ridge Road via Grand Lake.
It offers walks and magnificent views of this natural wonder without so many crowds.BTW -- I know it's out of the way, but I'd love to work the Grand Canyon into the trip too. I just don't know what there is on the North Rim.