Then too, museums acquire things for different reasons than do regular people.
An example is the test tube in the Ford Museum complex up in Dearborn, said to contain (as they say in the shipping industry) the last breath of Thomas A. Edison.
Total physical worth: $1.00 for the tube, less for the stopper. (The last breath is long time diluted, by the way - despite what happens when you wear your galoshes, rubber is not a completely impermeable substance, and gas molecules pass through it, albeit slowly)
Actual worth (to the museum, and probably to most others interested in the past); considerably more.
Even though it's a student horn, the fact that it was played by a famous jazz dude enhances the value all out of proportion to its worth to other musicians.
Put another way, while I would never buy a horn as an "investment", someone took a chance on that Grafton and realized a chunk of change. Their risk, their reward, and more power to them for moving something of marginal "real" value to a musician, but of considerable intangible value to the right party.