I think I have over-revised mine. I have read it so many times that it just looks like jiberrish to me now. Every time I revise it more, it seems that it actually gets worse! I kid you not! I just looked at an earlier revision and I liked it better than my current one, so I am starting again with that one. 😡
My advice would be to just leave it after being very confident with the draft you're on. Over-revision can be very detrimental; at the same time, several drafts are necessary and productive. It's not necessarily the # of drafts, but leave some Time in between each revision-- at least a couple of days to clear your head and read it as if you've never seen it before. If you can read it without being bored to tears or without it sounding like, "a very special (and sickly mushy) episode of Blossom," it should work out ok. Also, don't forget to get others to read it as well for different perspectives. Make sure they are people who will be honest and critical of it. Of course, all this advice comes from a fellow premed who is also applying for the 1st time this year, so take it with a grain of salt because I haven't had much experience with it. Jamier2, Tony C., and JD* would probably be of great help in this area. Good luck!