Fantastic job 4 runner. I as well have been going out there since the sixties. Don't go nearly as often as we used to gets so dang busy out there any more. Used to be just a sleepy little town. Seems some time in the mid nineties it really took off tourism wise. Even up until the early 90's The Needles District visitor center was a single trailer in a dirt parking lot with about 4 parking spots. You could hike all day or wheel and not see anyone else in there. Arches got all the attention. And as you mentioned they closed the river corridor camping for awhile. I was talking to one of the guys (well now I cant remember which agency it was) at the time about the closure and he told me it was just as you stated about overuse but the biggest issue was the visitors just plain pooped it out it just became to unsanitary to camp in the existing areas so as you know they built/designated camp areas with toilets.
The only thing missing in your fantastic write up was Canyon Rims Rec area. Not that there is much for people with travel trailers, motor homes etc in there but there are a few CG areas in there that are great for TCs or small trailers and certainly tents. Wind whistle campground I think is the only established CG in there but a fair amount of boondocking in there just not so much for trailers due to the access of those areas. A couple really good viewpoints overlooking the Canyonlands though you do have to drive quite a few miles to get to them.