If you have 45 minutes or so to kill in the car and you're interested in the topic of primaries, I encourage you to listen to this forum on KQED on the topic of California's Proposition 14, which comes up for a vote next month. (Prop. 14 would create a Louisiana-style top-two primary, in which all candidates of all parties appear on the same primary ballot, and then the top two vote-getters go to a runoff, even if they're of the same party.)
The forum opens with a brief interview with the PPIC's Eric McGhee (a friend and co-author of mine) about the possible effects of switching from a closed primary to an open top-two one. Does it make legislators more moderate and legislatures less polarized? Well, maybe. McGhee cites evidence suggesting that the effect would be small to nonexistent.
Then the forum turns to California's new lieutenant governor, Abel Maldonado, one of the main proponents of Prop. 14, and Richard Winger, one of the initiative's more prominent opponents. Maldonado's performance is, in my humble opinion, a trainwreck. He proceeds to list one complaint after another about the state government -- it's broken, it's broke, legislators are highly partisan, they spend too much time on silly issues, they can't pass a budget, politicians misrepresent themselves to voters, etc. -- but then says that the solution is a top-two primary. He never really explains how the latter would correct the former.
Meanwhile, Winger, to his credit, employs actual evidence debunking each of Maldonado's claims one by one. You say more open primaries would make it easier to pass a budget? Well, it turns out the budget was plenty late during Calfornia's use of the blanket primary a decade ago. You say it would make the legislature less partisan? Washington state used a blanket primary for decades, and their legislature is one of the most partisan in the country. And so on. And all Maldonado does is keep saying, "I've lived it. I've been there." And then he repeats his talking points. It's not a very impressive spectacle.
I've popped off on this topic before, but just to recap: I tend to be an advocate of strong parties. California's own experience with weak parties under cross-filing (1914-59) was not particularly inspiring -- the legislature was corrupt and easily swayed by powerful personalities and moneyed interests, and voters had no idea whom, if anyone, to throw out of office if they were dissatisfied. But okay, maybe you still want a less polarized legislature. Fine. Would a top-two primary get you there? Not really. The evidence we have suggests that the effect would be small or negligible. There turns out to be very little relationship between a state legislature's partisanship and the openness of its primary elections. Meanwhile, you'll end up with many runoff elections between members of the same party, giving voters not of that party a lot less incentive to participate.
Update: Typo fixed.