Normally, I'd be dubious of advice to conservatives coming from Ezra Klein, but I think he's right about the Paul Ryan for veep boomlet:
As vice president, he would be a soldier in the Romney White House — which most everyone expects to be cautious, pragmatic, and dominated by establishment figures. In the Romney White House, CEO Mitt Romney will set the strategy, and there’s little evidence that his instincts match Ryan’s preference for detailed, sweeping plans. So conservatives would have taken Ryan out of the House, where he’s proven himself able to drive the Republican Party’s agenda and force presidential candidates to sign onto his vision, and jammed him into a subordinate role in the executive branch, where he’d be duty-bound to fall in line behind President Romney’s agenda.
Conversely, as House Budget Chairman — or, potentially, Ways and Means Chairman — Ryan can be a conservative check on the Romney White House. They’ll have to negotiate their policies with him, they’ll be so afraid of disapproval that they’ll always get his sign-off first, and, if they try and end-run him, he can always go to the media or simply corner them by using his influence among House Republicans to send the Romney White House legislation that goes further than it really wants to go.
There seems to be an assumption that putting Ryan on the ticket commits Romney to pursuing Ryan-like budget policies as president. But once elected, Romney can do whatever he wants and Ryan will have less leverage than he had as a House Republican leader. Instead of elevating Ryan, this could marginalize him.
If Romney loses with Ryan on the ticket, it will set back the cause of entitlement reform within the Republican Party. The GOP will likely return to its "get the government out of my Medicare" demagoguery on the issue. And conservatives will be blamed for an electoral defeat they will have had little to do with.
The arguments for Ryan that make sense: he is the best defender of his budget plan, which there is no point in running away from. But this assumes that the best way to get Ryan's reforms enacted is to win a debate with Joe Biden rather than having effective congressional leadership. The shape of the Affordable Care Act owes much more to what could get through Congress than anything Barack Obama said on the campaign trail in 2008.