If you got a good essay and you have nothing else to add, why change it?
This comes up a lot. A lot of people reapply and talk about having to "rephrase" and "fixup" their essay. If your essay sucked so bad that you had to change it when you applied second time around, then there's reason #1 of why you didn't get accepted in the first place (you got accepted so I'm not trashing you specifically, I'm sure your essay is fabulous).
P.S. If a whole application cycle passes and you have nothing new to add to your essay, thats not good at all.