Although there was not a mass exodus of black people to the voting booths when Obama was on the ballot in 2008, there was an increase in minority voter turnout that hasn’t been seen in years. I think there would be an equally significant rise in voter interest if the issues of same-sex marriage or gay-couple’s rights were introduced for public vote. It’s not the same as the reaction that occurred in San Francisco, but I don’t think that’s a valid reason to not advocate the promotion of more rights.
for voter statistics:
http://pewresearch.org/pubs/1209/racial-ethnic-voters-presidential-election
J it might be worth looking at voting turnout in Georgia before they voted on gay marriage and the year the vote happened (2004, I think). I know it’s not a federal vote but it would be interesting to see if it had an impact locally.