<p>And is it a good idea to include a new letter in support of being accepted off of the wait list? Also, would sending in another essay (they didn't see my Common App essay, and I think it puts my application in much better light) be too pushy, or even start seeming desperate?</p>
If you feel the essay and letter will help, then you should send them. I would lean more toward the letter than the essay, if you feel you have to choose, but if you think the essay is very strong, then send it, by all means.</p>