Pittsburgh is still rebuilding the team after the 18 year losing streak, so they have to be careful not to mortgage too much of the future trying to chase glory this year. The team's offense has not been very impressive, but they've also been without slugging third baseman Pedro Alvarez for much of the year. If he gets completely healthy and produces anywhere near the level he did last September, he could be enough of an addition to this anemic offense.
Pence of the Astros is a two time All-Star who is not only a strong addition offensively, but one of the best defensive outfielders in the game. I'd rather see them go after a guy who they would still have some control over after the season instead of Beltran who would walk after the season. Beltran also has some history of being injured, the last thing you can afford to have happen if you trade away key prospects.
Some people question why the Bucs would be going after relief pitching, but you can never have a strong enough bullpen. Acquiring some more veterans for the pen could be invaluable down the stretch. Someone like Heath Bell could also have a lot of value if, god forbid, something happened to Joel Hanrahan.
In addition to the names discussed above, you might also be able to go after AAA players who are stuck behind major league talent. Someone like say Chris Davis, who could man 1st base and perhaps provide a huge boost in power. He's a risk though as he has struggled in the majors, but perhaps a change of scenery might be just what the doctor ordered. I'm not as high on this scenario, but given the Pirates budget concerns long term, this might be a better option for trying to add talent without giving up too much.
Some people suggest the Pirates should just stay still and rely on the chemistry that's gotten them to the top of the NL Central Division. Maybe that is the best option after all, but you'd also be banking on the fact that teams like Milwaukee and St. Louis will continue to play below their talent level. I'm not convinced that will continue.
No matter what though, this has already been a season of joy for the Pirates and their fans. Pirate Fever is spreading like wildfire through an old baseball town that has been starving for a contender for almost two decades.
Enjoy the ride Pirates fans! I know I will.