Matt Allen's Violent Roundtable on last Friday night is worth a listen even if only for the encouragement that there are such folks as Joe Trillo (R, Warwick) and Jon Brien (D, Woonsocket) in the Rhode Island House of Representatives, and there are multiple specific statements worthy of thought.
One suggestion that merits targeted comment, though, is the notion that closing the parties' primaries would lead the extremes of each to leave moderate voters with no attractive option in the general election. That outcome strikes me as hugely improbable. For one thing, it's reasonable to suppose that the sorts of voters who are inclined to participate in primaries in the first place would also be more likely than the average to take a moment to register for one or the other.
More importantly, the "extremes" of the parties will quickly learn that it's unwise to put forward the most pure candidates they can find. Rather, they'll favor of the most pure candidates they think they can get away with. That may move the candidates slightly away from center, but hardly to a choice between unpalatable options. Indeed, one could argue that it would actually give voters a real option.