Our current rig is a 27' model and a little over 25 years old. My wife would like to buy a 2013T Winnie Via(25' diesel) and spend the next two years or so revisiting the 49 continental states utilizing shorter stays and visiting more POIs. She would then sell and buy a 32' to 34'gasser with two slides for a more leisurely lifestyle, spending more time in fewer places. I specified 2013 as that was the time she fell for the little rig on the MB chassis.
I think that the money saved doing the more hurried traveling in a small diesel powered rig and the selling and buying a bigger rig would eat up any fuel saving as well as suffering the depreciation buying two rigs in a short time span.
Our Bounder has almost everything we want except a sofa and a street side sofa/dinette slide. I'd prefer starting off big and doing more leisurely trips from the beginning.
The structural things I would look for are fiberglass one piece roof and seamless side walls. We had too many leaks which have done some damage and cause many hours spent sealing seams that were covered up and replacing rivets and screws in poorly sealed areas instead of traveling.