I was a re-applicant for the class of 2009 and I chose to re-write my essays (both the AMCAS and the secondaries), mainly because they already have the old essays on file in admissions. Each school keeps a record of what you submitted and when I re-applied, my interviewers generally had a thicker folder than most. If your essays are excellent from the first time around, they will review them from your old file. Also, I didnt want to appear as though I had not put forth my best effort to address their concerns from my previous application year - I used the essays as a chance to directly deal with why I was rejected in the first place!
By the way, I know how hard it is to write those so please dont be discouraged. I was waitlisted at five schools the first time around, and the second round, I was accepted at four schools (three of which had previously waitlisted me) and waitlisted again at two. One more thing: I took two years off between application rounds - some problems (like applying late) are easy to fix and would probably not require changing your essays very much, whereas other problems (like a weak academic history) take longer!! Be realistic about your weaknesses and plan accordingly.
GOOD LUCK to you!!!! 🙂
