In what world has Nick Punto proven he can get on base? He's got a career on base percentage of .325.
It's also largely irrelevant. Aviles is clearly the better offensive package and his defense, while not spectacular, is good enough.
In 235 at bats against righthanded pitchers this season, Aviles is hitting .235 / .254 / .362
In 201 at bats against righthanded pitchers last season, Aviles put up a .229 / .263 / .338
All of Mike Aviles' production in the past two seasons has come against lefthanders. He has very, very bad against righthanders, especially in terms of getting on base. Using the sample size of the past year and a half, Nick Punto is a vastly superior option against righthanded pitchers. It is not even close.
Through 2010, Aviles was much better against righthanders, so perhaps this is just a 436 at bat slump. Or, maybe he's lost the ability to hit righties. Either way, there's not much reason to continue finding out, given that since Punto has gotten semi-regular playing time, he's been hitting as though 2011 was not a fluke. It's time to make the change. Even at Punto's career averages, he's a 60 point OBP improvement over what Aviles has put up thus far in his Red Sox tenure.
In order to argue that Punto is not a distinct improvement over Aviles against righthanded pitching, you have to believe that for both Punto and Aviles, the past season and a half has been a fluke.