Good read and thanks for doing this Ken.
I think certain music demands certain sounds. There are no rules but you know it when you are there. I'm mixing Chicago style blues for a new TV show. While it's not "amazing" music we have found that some things just seem to work. We don't record the harmonica through the C-12. It has more vibe through one of those sure Green Bullets. The guitar that really speaks is the mid "60's Stella guitar, tuned down a whole step.
Love reading through your comments and thought process.