There are sufficient tensions within the Repubs to warrant at least two parties, in the absense of the Democrats. But while half the country is wedded to the left, the gulf that separates us from them keeps us wedded to each other. Its a Jackie Gleason kind of marriage, the arguing never stops, but it contrasts well with the left where dissent is spookily absent.
Among the Democrats, the only debate is whether the US is evil, or really really evil. Whether the responsibility of the government is to meet most of life's needs, or all of them.
For actual reality-based intellectual energy and exploration you have to look to the conservo-libertarian side of the street.
The Democrats are the Abortion Party, and they have done everything they can to drive believing Christians and Jews out of the party. Now they are doing what they can to drive out any remaining patriots, and anyone with a personal moral code. Since the Republican Party is a fairly big tent, where diversity of opinion actually exists, we have been the beneficiary of this shift. When better days come, our differences will be sufficient to split us into several competing parties, and I look forward to such a time. Meanwhile, we are stuck with each other, and we are a fortunate, if somewhat noisy and cranky, family.