The Pirates won't be altogether quiet at the deadline. I expect them to add another bullpen arm, possibly an Octavio Dotel or Koji Uehara.
If they do add a bat, I would expect it to be the Cubs Carlos Pena, who they can acquire very cheap.
I'm no fan of Pena's, but acquiring him would come at very little cost. The Cubs want to get his salary off the books and the Pirates could add Pena for simply paying his salary and a low-level prospect or two.
While Pena isn't a huge upgrade over Jones or Overbay, he is a decent run producer that's not having a terrible season. While Pena is pretty much the same .230 hitter as both Jones and Overbay, he offers up more pop.
Jones and Overbay have combined to hit 16 homers and drive in 71 runs in 570 combined at bats, while Pena has homered 20 times on the season, to go along with 51 RBI in 312 at bats.
Perhaps getting out of Chicago would ignite Pena's bat for the final two months. If he could come over and possibly hit 15 more homers on the season than it would make sense if you could get him for next to nothing.
However, if acquiring a bat (not named Hunter Pence) means parting with any major piece of this franchise's future, then the answer should be a quick "no."
This is only just the beginning. This team will have better years in the future.
Stick to the plan.