Sounds like a fun trip. As for off pavement adventures, I can think of three I think you would enjoy. None of this is any secret and looking at a paper map of Baja these jaunts are pretty plain to see.
Looking at a map of northern Baja, the road comes south out of Ensenada. Less than an hour south is a paved fork that goes to the coast at Erendira. The pavement ends near the Pacific and you can turn south across a river bed to follow a track along the bluffs and beaches. There are a few homes and camps at first and then it gets more remote. You can camp along here if the timing is right. This road has several cutoffs that allow you to get back to the main highway. I would cut back over at San Antonio Del Mar, though you can follow the shore track for many more miles if it suits you.
Next I would strongly consider taking the turnoff for Bahia De Los Angeles, as it is quite spectacular when you arrive in the daylight. You can camp along the bay, wild or at various primitive campgrounds north and south of the village. The small town has plenty of places for tacos and beer, motels and a few small markets. You can spend the night and then head back the way you came but for the best off-highway adventure, continue south from there along the Sea of Cortez, on rough dirt roads that mostly go to remote fish camps. You go south a ways, before heading to El Arco where the dirt track then works its way back to the main road again at Vizcaino. One advantage of this detour is that it bypasses a few hours of the most boring and straight sections of the main road either side of Guerrero Negro and you get to see some still wild areas that few gringos ever see.
Finally, if you find that you have made it to La Paz and still have a couple days before the ferry I would head through Todos Santos to the Pacific and down that coast to Cabo. From crowded Cabo head east around the cape, taking the dirt coast road from San Jose Del Cabo all the way to Los Barriles. There you can decide whether to continue on the spectacular dirt coast road or hop on the paved road to zip back to La Paz.
