The fact that the Republican's are a fractured party and the Democratics, on the other hand, are lockstep zombies, suggest that there might be a little more serious thinking on the political right. Never trust a large group of people that agree on anything - or worse yet, that agree on everything.
To be fair, Dems mostly agree on basic things, such as equality, a strong middle class, women's rights, and science.
They've figured out that only a small portion of the right wants to argue against those things, and those people won't vote D anyway, so why not just go with what the majority of Americans want?
The Republicans used to be way better at playing the game than the Democrats. Now, I think it's flipped. Instead of "serious thinking" I would describe the Republicans who differ as pandering, just to different fringe groups. When they don't pander, they're more or less in lockstep with the Democrats. It's going to be a strategy that will pay off for the D nominee, won't have to tick toward the center when the general comes, whereas the R nominee will have to flip on a few issues.
As to the topic of the OP, I generally vote R because I believe that a free-market economy, when properly regulated, is what is best for this country. Over the last 4-5 years, it's been increasingly hard to find a GOP member who just wants to focus on that (or even do that, as many of them are just as bad as the Ds in spending, or in the alternative, are too anti-regulation for me). Most now are ticking so far socially right that I can't vote for them, as I don't want to support the government stripping away rights. Last 2 Presidential candidates I've voted for were Ron Paul and Gary Johnson. Not sure who I'd vote for now. Maybe Romney will jump in and avoid being a fringe lunatic on a few issues and then I can vote for him. Or maybe Jon Huntsman will come back. I'd be elated if that guy was the next POTUS. Outside of those two, and I'll probably write in someone.