I think if somebody specializes in a particular series, like .44 flattops or Bearcats, that it is neat to have an example in the collection with foreign proofs. But to me, stamping proofs on gun isn't much different than somebody stamping their initials in the bottom of the grip frame. It is an interesting subject for sure. Look at Luger collecting. Numerous models made at one factory, but different collector values (some super high) with proofmarks for the receiving country, depending on the contract.
Chet15