The Cards have already moved Carson Kelly to 3b and they seem to really like Patrick Wisdom.
Moving Carpenter back to 3b when he's proven average to slightly above defensively at 2b would be foolish. He's been one of the few players you'll ever see to actually make the shift up the defensive spectrum and somehow not take a step backwards.
As far as I'm concerned, Matt Carpenter is a 2b.
Adams and Wong for Tulowitzki? !@#$ing done. The Rox don't have a 2b to speak of and Helton's on the way out. I'd probably include an arm as well if they needed it.
Pick up Tulo and suddenly you have the 3-hole hitter that we need and possibly the premier defensive SS in MLB. Absolute worst case scenario is that he moves to 3b in 3 years to replace Freese when he departs.
If you can't draw a crowd, draw dicks on the wall.