Do Banana Plug Adaptors Degrade SQ?

No.

Just like any other connector type, they are just another connector.  Unless they are grossly underrated for the job they are assigned to, or corroded to the point where they do not conduct properly, all conductors are about the same.

Yes, but it depends on the quality. The quality we have now is much better than what was available in the past but even so, this is worth a read:http://www.tempoelectric.com/Wire_and_Cable_Facts.pdf

For what it's worth, I prefer bananas for their ease of use and the solid and stable connection I get.

All the best,
Nonoise

Any discussion on differences of connectors (i.e. "which is better") apart from being the same brand/manufacturer is a waste of time. The only proper assessment is with the same brand/model of cables with different connectors. I that context, spades are typically superior, but one would have to conduct a comparison with any given set. Adapters typically degrade. Anyone who dismisses such factors is obviously not seeking extreme sound quality.

In the scheme of the entirety of system building, adapters are just one of the many variables that influence the system. It is not absolutely necessary to have optimized terminations, but it will lessen the sound quality not to have them. Read my review of the Iconoclast Cables at Dagogo.com, wherein I comment on the difference between their banana and spade terminations. My finding was in line with the company’s position on the sound of each.