Hello bonazaberry. Welcome to the vintage Airstream community. The Sovereign
is the largest trailer Airstream made in the seventies, I think 31 feet long.
You have two questions. Considering the resale value of a 74 Sovereign
depends on many factors relating to its condition. The longer trailers are not worth as much as the short, cute ones. An old Airstream will have many needs, and maybe someone has renewed this trailer already. Tires, brakes, axles, frame, subfloor, plumbing, electrical, appliances, cabinets, windows, doors, body, etc. all have to be considered before any resale value can be estimated.
It seems like the 70s trailers suffered more from rear floor rot and "rear end separation" than other years. Some of the longer trailers actually have a buckling of the frame rails once the body separates from the frame. These are major repairs.
Actually, the floor layout is a preference of the buyer. If you went to the Airstream company website, you will find old trailer layouts. Maybe that is a starting point for bedroom ideas. I went to the local RV show and viewed many trailers getting some ideas for a make over of our dinette. It was worthwhile. We like our twin beds, others would prefer a large bed. Some like gauchos, others convert to reclining chairs. I don't think one layout is vastly more popular than another. It is just individual preference.
Hope this helps,