Hello George,
I might have some thoughts on the value of shinsa documentation. The value of shinsa documentation as you have already probably discovered is worth very little on its own. In your case, you have a gorgeous quality blade in polish with a clear signature. If you paid a fair price for the blade, it probably won't add much to the value to blade. The value of a sword is ultimately based upon the sword itself, although the NTHK papers are based upon the relative quality of the item. So, the grading sheet can give you a third-party expert opinion as to the quality of the blade.
But there is one notable exception. If you have a sword that is out of polish, has crap fittings, that you picked up for a song, and you take it to, say for example, the Chicago sword show and everyone laughs at you and tells you to not get your hopes up, but you did your reading and you did your research and you really believe in your blade. And you put it through the shinsa and it scores, say for example, 77 points, and people stop laughing at you and your rather hapless blade. The shinsa is so worth it. Not that anything remotely like this has ever happened to me.
Actually, I find that the best part of the shinsa is the grading sheets. Ideally, you should know as much about your blade as the grader, but the fact is that they have spent a lot more time looking as blades. They have an eye that can see things that you wouldn't otherwise notice. And even years later, I occasionally go through my grading sheets and learn new things about my nihonto. What I learn about my nihonto makes the shinsa worth it for me.
David.