Thanks for all of the tips, guys. Definitely a lot to think about.
I think leadership is probably an area that I covered pretty well. My GMAT score is above Darden's mean, so I don't think that I need to worry about that, unless I really want to try to get a higher Q in the bank. In the next few weeks, I think that I am too busy to mount a retake, but if my waitlist drags on into May or June, I might consider it.
In my application, I never stated that Darden was my top choice, though I did spend time discussing specifically how the case method would contribute to my future goals and be an excellent learning environment for me (though perhaps many people did that).
I think I will send them a letter, though I'm still thinking about what it will say. I'll post more when I have made some decisions. Thanks for the feedback, guys!