Does this offer a sort of land-grab opportunity where anyone who has an original recording can remaster it, convert to mp3, then claim copyright over that "transformation" of the original?
For more general answers, see this pamphlet from the US copyright office
There were a bunch of court cases about this, music radio, and rights payments.
I believe that is why Peter Kuran (Trinity and Beyond) patented a photochemical restoration process for revitalizing the color in films. Because his other restoration work is not protectable.