What Might Romney Hope to Gain by a Ryan Pick?

So Paul Ryan will be the vice-presidential nominee for the Republican party in 2012.  What could be some of the advantages of a Ryan pick?

• Ryan cements the loyalty of the "conservative" establishment.  Much of this establishment, in the Weekly Standard and the Wall Street Journal and various think tanks, have been skeptical of Romney but devoted fans of Ryan.  Now, this establishment can become top cheerleaders for the Romney campaign.
• Ryan has been able to win in swing districts before.  Ryan's district, WI-01, is a paradigmatic swing district, bouncing between George W. Bush in 2004 and Barack Obama in 2008.  In both 2004 and 2008 (and many other years), Ryan was able to win with big margins.  Perhaps Romney is hoping that will translate in the general.
• Ryan is a fierce debater.  Quick on his verbal feet, Ryan seems to relish to chance to spar with top-line Democratic principals.  The vice-presidential debate in the fall could be a chance for Ryan to shine.
• It changes the narrative.  The Obama campaign has tried to make this election about Romney's prior business experience and persona as businessman.  The Ryan pick could put a roadblock in front of this strategy.  With various signature policy proposals, Ryan might help change the campaign narrative to be about policy rather than personality.