I'm not an expert on copyright law but I am an expert on Photoshop and walk the "thin grey line" every day.
This statement, "...That said, were you to take an old photo and enhance it as I did at least one of mine, it is copyrighted. I've forgotten the correct wording for this but I asked at the US Copyright Office and was told so..." is probably incorrect.
It is called a derivative work and to qualify for a new copyright it must be different enough from the original to be regarded as a new work. Simpy restoring and/or colorizing a photo would not qualify.