Must See's between Salt Lake City & Las Vegas

If you are into steam locomotives Promontory Point is a must.

They have exact and very beautiful replicas of the engines.

Check out their website for schedules as to when you can see the locomotives in action. I love the sound of a steam whistle.

Point Supreme at Cedar Breaks is a lovely little CG for dry camping (at 10,000ft elevation). Last summer they had the best maintained state/federal bathrooms of any place we visited. Not too much hiking, but you can get some miles in mostly along the rim.

If you can't get a space at Point Supreme, Duck Creek has much more room (but is busier and noisier).

Snow Canyon State Park just outside St George is peppered with hiking trails, including some over petrified sand dunes.

Valley of Fire SP is first-come, first-served on camping so don't try the weekends unless you plan to get their very early and catch someone leaving.

With Zion, check map locations for the non-park CG's as folks as far as 30 miles away use Zion in their name. And this year don't plan on visiting Kolob Reservoir (road out of Virgin) as they have a major project causing closures.

I haven't stayed at Coral Pink Sand Dunes, but the area is other worldly.

On second thought, I think that you should drive over to Cedar Breaks. It is sort of like a small Bryce Canyon. I don't recall much hiking, just overlooks.
Some of my Pics.

Do you like art?
Check out The Spiral Jetty by Smithson. It is in the Great Salt Lake, not far from Promontory Point, UT mentioned above.

I would also include Valley of Fire State Park in any itinerary.

In the Salt Lake area, you might consider heading NORTH a bit to Promontory Point, where the east met the west with the transcontinental railroad. The National park Service has a very nice living history display there, and some interesting short hikes in the area. Northern Nevada is really pretty interesting - we really enjoyed our visit to Great Basin national park, but that might be a bit off your path... Also - a second for Red Rocks area just west of Vegas - there was a fire on Mt. Charleston a year or 2 ago, but there were some nice campgrounds (Forest Service) up there. ST

Thank you. Researching those suggestions now.
We have done Yellowstone & Tetons, need to get back sometime in the future.

this is in the wrong direction but grand tetons/yellowstone are mind blowing BEAUTIFUL!

Historical spots like Cove Fort might be a "different" sort of spot for a few hours' visit along the way.

I can't say I know if any of these are to your liking:

a) Minersville Reservation Recreation Site (whew) - that's west of Beaver
b) Dispersed camping East of Nephi @39.743527,-111.710868
c) Overnight at Black Rock road.. just before entering Nevada

I don't think I'd call any of them 'must sees'.

Zion is a must

Just south of SLC look up Mt Timanagos Caverns.