Comodave,
Understood, but I'm with C lectric on this one. Not because one would be unable to sell the boat otherwise. And, not because one would be able to sell the boat for more otherwise.
I do it for the same reason I answer questions any time the new owner of my last boat calls -- I want them to be as happy as possible, enjoy it as much as possible, and waste as little time and effort maintaining it as possible. I don't want them to spend time learning what I know. The past owner, and even two owners before that, of my present vessel have been enormously generous about that to me, too. So, does it take time and energy to answer phones calls or email, look up old records, stare at a wall and try to call back to mind what I once knew? Etc? You betcha. But, does it make the world as a whole a happier place? I think so.
I think of doing little things to document and preserve the boat for future owners in the same way. It is something that costs me that might make someone happy down the line. They might want the teak back (I would). They might sand it down in excited anticipation -- and discover that it was painted because it rotted, was filled, and isn't good anymore. That is a sad day. They might also sand it down and discover it is good wood, but has paint embedded in the grain and would need to be sanded too much to be restored. That is also a sad day. The first case isn't fixable. The second is.
A quick coat of varnish isn't expensive. It doesn't take much time. It may improve paint adhesion, depending. And, it can make someone really in the future happy. So, I'd do it -- then smile if they ever called me and asked.
And, heck, I'd be the first one sanding paint off rails. Just isn't my style. I know others have different taste. I've seen some nice rails painted. It is just one of those things where preferences differ -- so owners wanting to change wouldn't surprise me.
At any rate, I see where you are coming from. Makes sense to me. It is just that this "current caretaker" has a different point of view.
