Wood obviously has legitimate power, but his impressive-looking minor-league record is mostly the product of spending nearly his whole career in two of the craziest hitting environments in the minors - the southern portion of the California League (where he hit 43 homers as a 20-year-old in Rancho Cucamonga) and the Mountain-Time-Zone portion of the Pacific Coast League (where he logged a ton of time as a member of the Salt Lake Bees).
And even in those wacky offensive contexts, Wood exhibited serious strike-zone issues, often striking out nearly three times as much as he walked. That tendency has eaten him alive in the majors, and the awful numbers he has posted there probably aren't a fluke, as he now has 153 strikeouts and 13 walks in 172 major-league games. Those are the numbers of a guy who simply has no idea what he's doing at the plate. And the problem doesn't seem to be getting better. In 2010, he had 71 strikeouts and six walks; this year he has eight strikeouts and no walks. Wood at been at Class AAA since the Reagan administration, so it isn't like he has been rushed to the big leagues, and not once has he put up big-league numbers that show even a glimmer of hope.
Also, if you claim Wood, you've got to put him on the 25-man roster. So where do you put him? As bad as Ronny Cedeno has been, I wouldn't expect Wood to be better. And as little interest as the Pirates have shown in Josh Rodriguez so far, Rodriguez actually arguably has the more impressive recent minor-league track record, once you adjust for park effects. And since Rodriguez has some clue what he's doing at the plate, he has a better chance of success than Wood does.
I suppose you could also do something like option Steve Pearce back to Indianapolis to clear a roster spot for Wood, but at this point, I wouldn't bother. Pearce is a much better hitter.