Good discussion. Not to nit-pick, but re: your statement that Joplin incorporated banjo dominantly "thereby telling us that bluegrass too is African-American." I believe that claiming Bluegrass is afro-american because it incorporates an instrument developed by afro-americans is like claiming jazz is european because it incorporates trumpets and coronets. Each instance is more likely an example of people using available tools to perform a kind of music that was native to them. For Bluegrass, I think a much stronger case can be made that the banjo was incorporated as a well-known, portable instrument that could be used in playing melodies of a principally Scotch-Irish or English origin.