I'm a reapplicant. I used the same letter writers and added one new one this year. I wrote out exactly what had changed in my application, sent them it, and met with each writer to discuss these changes and just generally reapplying. I told them to feel free to modify the letters they had written me last year. I had strong LORs last year and even stronger ones this year - almost all my interviewers made comments.
However, I'm sure people have reapplied and used the same LORs, PS, secondaries, etc. and still gotten in. I just felt that I had changed a lot as a person and I wanted to showcase that, so I got new-ishletters, rewrote all my secondaries, and completely started over with my PS.