If they are taken care of, silver can be polished to almost like-new appearance. Not so much with lacquered brass.

I suggest with Sousaphones you invest in the fiberglass coverings that attach to the bottom bow of the instrument [I believe they are called "Sousa Savers"], where the Sousa is most likely placed in the stands, etc. when not in use. The leather (or leather-like) coverings only prevent scratches, not dents. We had a set of Sousas that had to be repaired due to dents and holes created in the area where I mentioned above. They don't make these instruments with the thickness of metal that they did many years ago.

Looks might not mean as much to us adult musicians, however to an adolescent it's a big deal.