I'm not sure what the probable gain for Romney is to pick Ryan other than that it puts the Ryan style budget front and center and he now creates a further "technocrat" aura around his campaign. There are a lot of problems with this approach.
1) Ryan's Congressional record isn't very promising for technocratic budgetary sense. He voted for the whole mess of Bush-era bloat that increased deficits rather than decreased them. His justifications are partisan (I was being a team player), which are not reassuring for the supposed Romney-ish view of doing effective things instead of partisan things.
2) Some economists like some of the more important conservative annoyances (TARP or the auto bailouts) that are being overlooked by those same conservatives now and while I don't like the particulars in the Ryan budget proposals (for instance it hands-offs the defence budget from cuts and doesn't do much actual tax reform in favor of tax cuts), I do like having someone around who seems willing to approach the third rail topics of entitlements and long-term deficits.
2a) It makes more sense to leave a wonkish person like that in Congress, where they can help pass legislation being on a budget committee in the House and not in a useless ceremonial position as the VP.
3) There isn't a constituency for technocratic views or its counterpart of governing competence in evidence on the right and left-leaning voters motivated by such things are apt to be more skeptical of either Ryan or the GOP in general or live under the (somewhat) misguided notion that Obama cares about such things and is only being stymied by the GOP's obstructionist views. There is little crossover gain to be had here and little enough in terms of actual conservative rallying to be gained. Wonky views and complicated talking points aren't likely to inspire crowds of conservatives.
4) It might put Wisconsin in play for Romney now but I'm not sure Wisconsin is significant enough to matter to the general election this year. Most evidence suggests it was Ohio or Florida or Virginia that are the cornerstone states in play, with states like Colorado at interest and risk for Obama and for which Ryan does nothing to assist (he's a more ardent drug warrior for example on the Colorado problems for Democrats, he doesn't do anything for Florida, and Ohio's a weird place).
5) He is young and thus appealing on that front, but a young idealist with muddled Randian notions isn't likely to appeal to independent voters. It might appeal to some Paulite voters, but Ryan's civil libertarian views are so poor that this is unlikely. It's possible that his relative silence on his social conservative views will mean those issues could go ignored, but I doubt it. They've already been issues front and center throughout the campaign and Obama is a capable campaigner unlikely to ignore any issues that he might draw an advantage. Younger independent voters likely to respond to a fresh face (as they did with Obama), aren't socially conservative (for the most part) and are thus turned off by the impression of the GOP as such a party.