Here's the thing; there's a huge rift between purists for whom "the Blues" is what guys like BB King and Muddy Waters were playing in the 50s, and "evolutionists" (or whatever you want to call them) who would accept music inspired by that stuff as the "new blues." Basically it's a matter of whether you think that guys like Bonamassa and Gary Clark Jr. and for that matter Jack White and the Black Keys are carrying forward a living tradition, or if you think they've bowdlerized it or ruined it or whatever and aren't playing "real" blues. If you don't accept what those guys are doing as "real blues," then blues has pretty much stagnated, and it's impossible for it to be otherwise - because if people keep playing like they played in the 50s, blues "hasn't changed/grown", and if they don't keep playing like that, it's "not real blues."
Personally, I think that we forget that the blues is a marketing label used to package artists for sale to audiences. Back when the recording industry got started in the 1920s, if a black musician came in and recorded a song, it was labeled "blues." If a white musician recorded the same song, they labeled it "hillbilly" or "rockabilly" or something of that sort. The music world actually got more segregated than it had been, and the musical styles diverged from each other, because of the record companies pushing artists at same-race audiences.
I think once we realize that, and get over the starry-eyed mystical Mississippi Delta/jungles-of-africa myth, and see that "blues" is just a marketing label, we can listen to and appreciate artists influencing each other much more freely.
