I would sell mine with my layout if there was an intereseted party. BUT I would put lots of caveats on it. I built it and I can maintain it and I tried to keep wiring diagrams and notes on everything I did. However, realistically, it would be a bear for someone to come in and try to take over and maintain my layout. and they would probably not like my workmanship either - sometimes I don't even like it!
I don't think I would buy a house with a layout. I have specific ideas of what I want to do and it has to be an operations focused layout, not a display layout. I have not need for continous running but lots of need for industrial sidings for example. So I doubt I would ever find one that would interest me. And then I would have the same problems taking over someone else's as they would have with mine.
Now if your find one and like and the DOCUMENTATION IS GOOD enough for you. - - go for it.