Honestly, I don't think any upgrade over Nava is going to help this much anywhere as much as an upgrade in the rotation. Assuming Upton is out of the picture, the next options aren't pretty. The Sox wanted Jones in the Hanrahan deal and were turned away.
Hairston is the next guy on the list. With the price he is asking for, I would much rather stick with Nava, and add some quality pitching depth.
Marcum and Lohse would be nice, but Jurrjens, Pavano, Vasquez, Oswalt, Saunders are still out there as well. I'm still okay with longshots like Braden, and Wood getting minor league contracts as well. And Brian Wilson won't be available till mid-season, but could you imagine that bullpen?