Brett Wallace was a large price to pay for a guy who isn't performing so well this year and is a free agent at year end.
Matt Holliday was definitely a fantasy stud in Colorado but then again almost anyone is outside of pitchers. Does giving up top prospect Brett Wallace who is already paying AAA ball really worth it? This move also pushes Colby Rasmus to the pinch hitter status just as he was really hitting the ball well.
The move does show they want to win this year and I can't blame the team for getting more protection for Pujols. However I don't think a bat is what they needed. Without Brett Wallace the Cardinals officially have no chance on acquiring Roy Halladay.
They've now shown they want to win so keep an eye on this team making some other sort of move for a starting pitcher. It would probably be more of the Doug Davis or Jarrod Washburn type however since they don't have anything else to offer unless they're willing to move Colby Rasmus.
In the end this trade helps St. Louis now with the worst case scenario being they get two type A compensation draft picks if they can't resign Matt Holliday.