I favor the top-two system, but not because I think it is some great cure for hyper-partisanship. I just think it gives voters better choices. For example, if you live in Oakland, California, why do want to have an election between Rep. Barbara Lee and a Republican? What’s the point? Rep. Lee is going to win with 80% or more of the vote. But how about she has to face a green party candidate in the general election? Now the people of Oakland can have a debate between two people who both might be acceptable to them. The same thing is true in some of the farming districts on the Nevada border. Those constituents might prefer to have two Republicans debating policy rather than having to listen to a Democrat who has no chance. The top-two system also makes it easier for third, fourth or fifth party candidates to get on the primary ballot, and therefore easier for them to get heard. They are much less likely to act as spoilers that harm the most viable candidate on their side of the right/left divide.
Most important than the top-two innovation is taking redistricting out of the hands of the politicians and putting it in the hands of a independent citizens board. Despite being the biggest state with the most congressional districts, and despite the massive turnover in the 2006, 2008, and 2010 elections, California lost almost no incumbents in that period. Most of the members they did lose, they lost to aging or scandal. But, in 2012, after the redistricting and top-two system were in place, there was quite a lot of reshuffling.
I don’t know how much these changes can improve the national political divide, but I like them without regard to that. I think California is functioning today primarily because the Democrats have supermajorities in the state congress and Jerry Brown is the governor. If Obama had those kind of majorities, no one would be talking about partisanship and gridlock. They’d be talking about progress.