I’ll answer my own question (in case someone else is thinking of headed to Johnson Valley for the first time). Yes, there are miles and miles of easy, intermediate, and difficult trails in JV. We entered on Granite Road, near Cougar Butte, and found lots of rocky trails to play on a couple miles due east.
After a couple hours we headed south, got on the 247, went east, and reentered JV at Boone Road. We found the Hammers area east of Means Dry Lake. Not exactly sure which of official trails we saw (no one else was in the area), but we found numerous trails way more difficult than we were prepared for. We also found plenty of trails that were just the right challenge for us. Next time we will do a loop around the entire range (Hartwell Hills). A great place to spend the day exploring. We entered via Victorville/247, went home via Yucca Valley/247 (about a 2 hr drive for me).