I am with you that these music sheets should have been preserved --
perhaps put in a special file for antique embarrassments of this sort,
but kept. There is research value to them, social history that should
not be lost, and the lessons of that history.
On the other hand, there is a huge collector market for this stuff,
mainly among African-American collectors, in fact. A friend funded
a large donation to an inner-city social services agency by selling off
his own unwanted toys and ephemera of this sort back when eBay was
a little less restrictive in what could be sold.