Assuming Wainwright's finger is now fine and he comes back after a few rehab starts, in which role does he help the team more, Closer or Starter. At first I thought this was pretty obvious, but now even Bernie has gotten behind this so obviously there is more merit to it than I thought.
Wainwright for Starter? The main point is very simple, wainwright would pitch 7 innings per 5 games as a starter, but won't even get half that as a closer. Wainwright gets about 4 outs more per game than Joel PIniero, the pitcher I'm assuming he would replace. That means that aside from maybe his first start back he takes stress off of the bullpen just by starting, so you can have your cake and eat it too. There is no need to transition Wainwright back to a starter, which becomes absolutely neccesary I think when you cut down to 4 starters if you make the playoffs, 7/4 innings per game of Wainwright is too good to pass up. If the Cards get a little help from off days and the arms are healthy, it might be a good Idea to switch to a 4 man rotation the last 3-4 weeks of the season if they need to catch up to another team.
Also, you have to consider that Izzy will still be there, I have a hard time believing Wainwright would boot Izzy completely off the team. So while Izzy might not be able to muck up any high leverage situations, he'll still make you uneasy and probably won't provide that many innings as I see him getting lifted early and often. I think the main reason why people want Waino as closer is they are just tired of the whole Izzy/Franklin fiasco, but they'll still be there.
Wainwright as a closer? He'll only be brought in for close game situations, which are higher leverage than the average inning he starts. Also, his ERA should lower (but then again so should Joel Piniero's) if he only has to pitch 1 inning at a time. And most importantly, we won't be blowing so many friggin games in the 9th inning.
That's about all I can think of, I'm sure there are lots of points that can be added. I feel the ideal situation is to DFA Izzy (tastefully if possible) and call up Perez. KMac moves into the closer role if you believe that the best reliever belongs there (I believe you just go for the highest leverage situations and there isn't much special about the last 3 outs).