If it didn't work last year, I'd say start over. You can always incorporate similar experiences or ideas, but a fresh essay would be a much smarter play than a modified version of an old one.
I reused mine, no problem. I didn't even modify it. Mine was also a GPA issue, so very doubtful it was ever read. Definitely find a few "mean" people to review it if you didn't do that last year.
I don't think you should necessarily start over, but definitely re-read it and make some modifications. Have as many people as possible took over it and get feedback! Chances are if you had a lower GPA then the essay probably wasn't read, but doesn't hurt to make the essay stronger.