Allow me to play devil in a blue dress for a second-
I really don't like this trade because :
1. The Astros now have a weak defensive outfield. Lane doesn't have the range, Burke doesn't know how to play outfield well enough. Lee, Scott, and Burke might be the worst collection of outfield arms in the National League. I haven't seen Pence, but everything I've read says that he's a left fielder. Great defense up the middle was a huge part of the Astros' runs in '04 and '05.
2. Hirsch looked pretty good. He could develop into a middle-of-the-rotation innings-eater just like Jennings. Although it might be a bit tough pitching at Coors as a fly-ball type.
3. Only one year of Jennings. He's going to be a free agent for the first time, and with salaries the way they are, he's going to want to test the market. Yet the Astros lose a starting CF, a top flight pitching prospect and another possible prospect, for one year?
Of course, it's impossible to fully judge this deal, and even this off season, for some time to come. Hopefully there's a deal out there for a good defensive CF, this team badly needs one.