IMF cannot be the independent central bankers' clubhouse
You mention a lack of credibility and legitimacy but seem to believe this could be solved by giving the professional staff a free rein. It is much more difficult than that. One of the reasons the IMF has lost credibility is in fact the mistakes of its staff and these go much further than the handling of the Argentine debt crisis. If you take a closer look, you will find them backtracking on so many of their "cast-in-iron" policies. The world needs not less accountability in the IMF, but much more.
In my view the Fund's problem is that it has now turned into the clubhouse of the "independent" central bankers. What instead we need the IMF to do is to open up its executive board and diversify the recruitment of its staff so there is a better chance for the board to have a healthier perspective of what the IMF's role should be.
Though I agree completely with you that the top job should not be reserved for a European, since "he must now defend interests wider than those that put him in place", may I also advance the idea that it should not be reserved for a central banker either?