tatest - you make some important considerations regarding the idea of keeping a single RV for a lengthy time frame. I have seen a lot of friends, relatives, etc. who started out with a small TT, TC, or popup, and then moved into a 28+ foot A or C, and then moved back down to a small C, B or TT. Their lifestyles changed over the years enough to necessitate the changes. Similar to home buying historically. The difference from the home buying trend is that with an RV, most people go to the bigger units when they become empty nesters (whereas with housing, the go bigger when the kids arrive).
I do find it interesting that a lot of clipper owners have actually owned them for longer than expected. They bought them when the kids were young and have kept them well past their empty nester phase. One of our club members is 81 years old now. She and her husband bought their clipper brand new and she only sold it when her husband died several years back. She still attends the rallies - sleeping in a tent surrounded by clippers. That dedication for a 21 ft Class C is common among clipper owners.
Which leads me to this thought. I think RVs have three eras: new - it's exciting, up-to-date, on the edge, etc.; old - it's outdated, drab compared to new RVs, etc.; and classic - it's passed the point of old and has a retro-ness that is refreshing.
If you can manage to keep your RV through the old era, then you will likely keep it until you can't drive it anymore (whether due to your inability or the RV's inability).