Since you are looking at a 4 hour car ride each way, have you thought of doing Arches, Moab & Canyonlands NP? It is about 40 miles less each way (about a half hour less each way). A couple of years ago I also saw McInnis Canyon NP in Colorado, it was a nice park, but wanted to visit during the spring or fall (it was a very cold January).

Of course, you might want to check the passes if there is still some snow.