I think you are asking for backcountry roads not spots to visit. Capitol Reef has quite a few good 4WD roads, I really recommend the Hartnet/Cathedral Valley loop. It's about 70 miles plus or minus depending on the exact route one takes of isolated and not much visited country with spectacular scenery. The road is a good gravel surfaced road with some shallow water crossings. There are endless boondocking opportunities:
Capitol Reef backcountry roads..
The Burr Trail is another good road with slot canyon access and lots of camp sites.
The South Draw Rd is one to keep off off unless you are driving a jeep sized vehicle. We took it not knowing what to expect and had 5 miles or so of white knuckle driving over a muddy dirt ridge barely wider than the truck with several hundred foot drops on both sides of the trail. And when I say barely wider than the truck I'm not exaggerating. Opening the truck door you could look straight down the drop with maybe a foot or less on each side of the tires. The trail surface was mud and I don't mean mud over rock either and did not provide a firm road surface...heh.
Somewhat further afield Escalante provides access to many 4WD trails including the excellent Hole in the Rock road, 70 miles of good gravel road in BLM land with some excellent camping spots like Dance Hall rock:
BLM Photo