Jim Bowden argues that the Pirates should sign Andrew McCutchen to a long-term deal, which is the first piece of evidence I've seen that suggests the Pirates shouldn't do it. Snark about Bowden aside, though, it's actually a pretty good argument. One of the reasons he lists for signing McCutchen now is that it would be bad for the Bucs to wait until McCutchen has the big breakout a lot of us are anticipating, which would raise his price considerably. Also, he notes that the Pirates don't have many financial obligations to worry about after next season, and are therefore in a good position to be able to afford him.
It seems weird to be talking about this when McCutchen has made some very strange plays recently, like the failure to run out a strikeout last night, or the baserunning gaffe in the Astros series. But here we are, and a couple of unfortunate plays in the last few days shouldn't really change the Bucs' ultimate goal here.