I have been camping for 25+ years, all over eastern and southern USA, size of unit has never been a real issue.
Everytime the size issue comes up several folks are quick to note that the larger the coach the less places to be able to use it. I think that this is to a large extent overblown and unrealistic. There almost always will be RV parks within a few miles of any attraction that can accommodate any size RV. Why limit the size of your RV just to be able to use a specific campsite or two that is very small. Going into retirement, the OP most likely will be traveling quite a bit and can simply pass on the smallest campgrounds for ones with larger sites that accommodate the larger coach.
As retired folks, the OP most likely can benefit from the room of a larger coach if for no other reason than to be able to have some personal space, spread out, have the kids/grand kids camp with them, carry more stuff, etc. Room is almost everything inside the coach when spending lots of time in it.
It would have been interesting to have been able to differentiate the thread's responses by those not retired and those that are retired. I think the campsite size issue for retired folks spending weeks or months in the RV would pale in comparison to the need for interior space, amenities, and interior comfort. For young folks that just have to camp in
the site next to the lake or creek, no other site will do, then the RV size might be a greater consideration.