Wow, thank you all for such informative responses. Here's some more information about the score:
I'm assuming it's an autograph, not the manuscript.
It's definitely not the manuscript. It's also not an autograph similar to those in the Amazon link. I think it is what is considered a conductor's score of the whole symphony, about the width of a pencil.
The message reads:
"To Joseph Maddy, a great man doing a great work. From his octogenarian friend Edgar Stillman-Kelley, New York, Jan (?) 1937"
It was once in a library so it has a library barcode and stamps on it and such.
What if you donate it to a university/conservatory or some place that will take care of it and let everyone still have access to it?
Do you think unis/conservatories would be interested? I think it makes sense for Interlochen to want it most, considering it was addressed to their founder, but they sold it in the first place so I'm not sure they'd want it back.
I do enjoy owning it, but it just sits hidden in a drawer most of the time. Maybe donation is the way to go, unless it will increase in value with more time?