Quartzsite can be as crowded or as uncrowded as you choose, there is tons and tons of land to camp on. You get to pick your own spot. I never really seen any problem of dogs running wild.
For some good info and boondocking spots down there check out the winter archive posts in @SteveandDianne Steve and Dianne’s blog They spend a good deal of time around Quartzsite. http://steveanddiannesmostexcellentadventure.blogspot.ca/
Another area I really like is right around the town of Borrego Springs, CA Beautiful scenery and very laid back. There are a few posts on my blog. http://www.loveyourrv.com/?s=borrego
It’s a decent day of driving in the RV, maybe 6 hours or so if you stop for lunch, around 250 miles. Also quite hilly as you drive through the mountains and then down into the valley where Scottsdale is.