Personally, I just edited my original essay. The main idea stayed the same, but I reworded some stuff to make it more clear etc. I also added one more example from recent clinical experience to make it sound better.
I know that some people use exactly the same PS and still get in. Some people decide to completely restart from the scratch, some people just "edit" things.
I called my state school to ask why I was waitlisted (or more like what can I do to improve my application).
I was told that my PS was not the problem. I did revise my PS by working with my premed advisor, my friends etc. I do think that my PS sounds much better, even though it is clear that I revised this essay based my previous personal statement.
I guess my advice would be, YES you should edit it. However, it is hard for your "why medicine" to change drastically in one year. Personally, I don't think you need to completely rewrite it, but I think there are always ways to improve.