When I started shopping for a truck and camper combination, I really wanted a 4x4 but I came across a deal that was too good to pass up though and it was 2WD. In retrospect, I think I'm pretty happy with going 2WD, especially on the 7.3. I get the gentler coil over suspension up front instead of leaf springs plus a better gearing ratio for highway cruising and I also gain a few hundred pounds in payload capacity.
As I'm contemplating purchasing an Expedition Max (expanding family) I'm faced with the same dilemma. We will be purchasing used so this decision might be made for me just based on what is available. If I had my choice though, I think I would prefer to get the 4WD but with the gearing of the 2WD (I don't think this is possible). I get why they put lower gearing on the 4WD but the loss in MPG over the life of the vehicle I don't think justifies the one or two times in a lifetime most people might need that extra low gearing ratio.
In California, I think 4WD is more of an option than a necessity. Our weather is so mild on the coast and valley that it is unnecessary in my opinion. The only reason I am contemplating 4WD for the Expedition is for the few times we might be in the Sierras during the winter coming over a mountain pass. Rare if at all but still, if I'm spending the money, might as well be prepared.
In regards to the 7.3 that is 2WD and carries the camper, I've been to Pismo Beach many times now and only got stuck the first time I went. All the others I just air down to 15-20 psi and I have not had a problem yet. As someone else already said, a camper isn't optimal for the types of off-road conditions that might really require 4WD.