I promised to follow up with a trip report so here goes.
Joshua Tree: We used the Black Rock Canyon campground as our base and would do this again. Nice views from the campground, great hiking trails accessible from the campground, and decent bathrooms with water (no showers). Joshua Tree is such a beautiful park. Our favorite hikes within the main part of the park were Hidden View and Jumbo Rocks.
Anza Borrego: We booked 5 nights here with hookups and didn't want to leave but were lucky enough to get one of the camp host sites for 2 nights over the weekend to extend our stay to 7 nights. Even most non-hookup sites are quite beautiful with views and cool palapas. Next time I would do 10 nights or even 2 weeks. Favorite hikes were the Oasis trail, The Slot, and the nature trails near Tamarisk Grove. Oh, and the Pictograph trail.
Everyone at both the above parks (rangers and campers included) were so happy and friendly. It was such a great escape from the real world to see everyone get along!
We didn't go to Idyllwild due to wintry conditions and skipped Julian for similar reasons. Next time we'll visit these places as day trips rather than plan to camp there.
San Elijo (San Diego): We stayed here our last 6 nights in a site right on the bluff. We didn't get around much here as we spent a lot of time visiting with our daughter and her friends. And of course there was that beautiful ocean full of surfers to watch!
What a great trip we had. We didn't get to a lot of the places we thought we would (ex. Red Rock Canyon, Idyllwild) but there's always next year right?