The "Opportunity Cost" is the value of the alternative not selected, and it's not limited to the dollar amount of the running maintenance and expenses. I had a Pathfinder and took it off raod and camped in it. Nothing technical, but off the fire roads. It is bullet proof. I also had a Safari AWD, Never camped in it like we talk about here, but spent many nights in it and 18+ hours at a stretch. Never took the Safari really off road, but out in pastures, some woods and along creeks, if you call that "off road".
The Safari was hands down the more comfortable of the two alternatives. I could duck walk around and move about bent over. In the Pathfinder (or any SUV of its size) you'll be crawling or slithering in and out. The van has more usuable space. MPG is about the same, the GMC maybe a little better. In my area, the Pathy will cost more than any Astro in comprable years and condition. Either will tow about the same. High winds on the highway you'll be fighting more in the GMC than a Pathy, but it's not that bad (if it gets that bad you should probably get off the road anyway!) I would say that bigger is better in this comparison.
While the opportunity costs can be measured in dollars to some extent, the cost of seeing the doctor about my back is another issue. IMO, the costs of comfort lost in any SUV compared to a van are much higher....and the same thing goes again if we compared a van to a motorhome. If you're a hard core offroader, I'd suggest the Pathfinder or like others a good SUV, if you lean more toward the camping and livability ov the vehicle, with some offroad abilities, seems the GMC/Astro would be a better choice, even without a top.