While the aura of the actual document may be a draw for tourists and sightseers to museums, it is not of any actual importance whether they have the real object. The details of the documents can now be captured and digitalised meaning that any value that can be derived from them for academics and enthusiasts can be done so without access to the actual object.
We all want relics to end up in museums, but the reality of it all is that there is not enough resources for these materials to end up in the right hands. The scarcity should drive up prices, meaning those that purchase these goods should have the money to maintain them as well.
Historical documents need to be preserved in museums for public use. This is because if they are preserved individually access to them will become greatly restricted. It may also lead to loss or destruction of this documents if they are not properly preserved. This may eventually lead to the documents contents being lost for good and even forgotten.
Private ownership is of importance. There is no doubt about that. Anything of public consequence however should be kept in the public's hands. It is understandable that if someone owns a document passed down through generations, it still belongs to that person to do with what they wish. Such a person should consider, at the very least, selling the document to the public for display in a museum.