How is it irrelevant? It's as relevant as Bayer and Volkswagen's Nazi connection. Southerners didn't join the GOP because of racism. Don't believe me?
Exit polls from the 70s and 80s consistently show that the most Republican voters in the South were young voters, not former Dixiecrats. And the South continued to elect Democrats long after the CRA was passed.
http://www.claremont.org/crb/article/the-myth-of-the-racist-republicans/http://www.nationalreview.com/article/386257/myth-republican-racism-mona-charenhttp://www.nationalreview.com/articles/300432/party-civil-rights-kevin-d-williamson