I agree with your assessment of the film as "a grown up view of leadership". Batman, Dent, and Gordon employ Machiavellian leadership in large supply in order to catch what they see as a larger menace. For them, the ends (catching and/or killing the Joker) definitely justify the means (wiretapping, kidnapping, torture, distorting facts/manipulating media and press, doublecrossing, baiting, and good ole-fashioned assault).
Many adults still expect their political representatives to be effective leaders and still be completely within the bounds of law, clean cut, sober, and honest. This film is, as you put it, a grown up view of leadership. Gritty, ugly, and often destructive as they may be, we gotta have leaders.
I like this Batman because (action sequences aside) he is realistic. He's about 60% virtuous, 20% selfish, and 20% vengeful. He is dedicated and not at all above getting his hands dirty. But he still has his "one rule" that he simply will not break--he just won't kill people. The strange irony is that he refused to kill the Joker (a MASSIVE threat), but kills Harvey Dent saving Gordon's son.