Ironman,
You are correct that they are not really "offroad" vehicles, but I'm not sure if the 4x4 sprinter is either. Kind of long and tall for tight trails.
I'm no expert but I think the modified Astro's, Express Van's, and Ford E series are about as big as you want to go if you really want to get out there, and the Landrover and Jeep guys would say they are too big.
I had an unlifted Astro and the Promaster has better clearance. BTW you can put larger offroad All terrain tires on them, not sure how big, but bigger than stock. A guy here is Dana Point has done this.
I can get to most of the places I want to go in Baja and I kind of fly under the radar. A huge lifted vehicle with lots of gear hanging off of it kind of stands out in Baja.
BTW you live in Paradise, really like that stretch of coast.
John