I believe that Sneed is one of the most complex and realistic characters in animation. Although on the surface he appears to be nothing but a redneck, if you actually watch the show and read between the lines, he is a lot more.
Sneed, and by extension The Simpsons as a whole, is at its core about showing that one group is not always right, and one group is not always wrong. It's not just blind liberal bashing by some angry Texans, or angsty liberal bawwing like Family Guy, it's somewhere in the middle.
Sneed is a man who represents traditional family values. He works a blue-collar job, has an ugly Chuck, and a soil pH he fails to understand. He enjoys selling his seed, feed, and gummy bears.
Because he represents traditional values, he often butts heads with newer, more liberal ideas. Now about half the time, he will have a hard time adjusting, but ultimately realize that it isn't that bad, or is even correct. But the other half of the time, he exposes it for the bullshit it is and tries to save those who have been brainwashed.
And that's the thing, Sneed isn't a racist or homophobe, or even a devout Republican. If that was the point of the show, he would have voted for Bush in that one episode. No, Sneed is a good man who just has a hard time adjusting.
Sneed stands by his family, his friends, and his family values, and this is why he is a good character. He has a hard time understanding his soil pH, like a lot of farmers, but ultimately loves it and eventually seems to accept it for what it is.
When you really get down to it, Sneed is so much more than your average sitcom farmer. Unlike the bumbling Homer, he is a very real man who many people can relate to THEIR farmers. He is the next progression in both mature cartoons and sitcoms, a complex character, not a 1 dimension caricature.