I first went into that country (SE Utah) in 1959, and beat my way with an old Ford truck between Torrey and Boulder along a dirt road that is now Route 12 in the autumn of 1963--- just after running Glen Canyon before it was flooded. It remains one of my favorite parts of the West and I try to return every year--we are going again in April.
Yes, the light pollution around Boulder is limited, but as you no doubt noticed, there is a lodge there (Boulder Mountain Lodge), gas stations, etc. The area you mention, between Boulder and Torrey, gets my vote as one of the finest places to observe in all the U.S.---9,000 feet plus, campgrounds (in summer only), and magnificent views over the canyon lands. Try the area around the Steep Creek overlook. In the old days you could see the towers in Monument Valley from the point where Route 12 turns north beneath the rim of the Aquarius Plateau. There are a number of little two-tracks around that allow free camping--crash anywhere you want places. In my experience, the only time anyone stops is to ask if you are OK--mainly ranchers, or, in the fall, hunters. That part of Utah is very safe.
Other good places in the general area are:
South from Henriville toward Cottonwood Canyon (nice slot canyon walk).
Down the Hole-in the-Rock road south of Escalante. You can do the first 50 miles in a car, though some of the side roads may require more clearance. After Davis Gulch it is definitely 4x4--my wife walks most of the way. Ask about conditions at the Monument office in Escalante. Can be very muddy after heavy rain.
South from the main campground in Capital Reef down a good dirt road until it crosses a grim looking creek bed--Pleasant Creek, again, 4x4 (great Indian art up creek on the right). I usually park just before that in a large open area by a corral. Also good sites down the Notom road, and a NP campground at Cedar Mesa. Perhaps the best--if you have high clearance, is the NP campground at the top of the Cathedral Valley--quite high--7,000 feet? Requires fording the Fremont river but tourists do it all the time. Again, check with the rangers in Fruita before you go.
Off Route 95 toward the Maze ranger station. Dark, dark, dark.
And Goblin Valley--nice campground.
Bridges is very dark but sort of boring if you are not observing.
That should take you awhile
. If you want more info when you go, just PM me.