FWIW, I was an OK (AOA, mult. publications, very strong recs, good Step 2 score) but not top notch (unknown med school, average Step 1 score) applicant to a fairly competitive specialty.
I did a second look at my #1 choice, but only since I genuinely wanted a closer look at a program. It was my last interview, and I went into the interview thinking I didn't have a real chance of matching there and not expecting to like the place that much (had a malignant reputation). When I got what I perceived to be some positive feedback after my interview, I figured I owed it to myself to take a closer look so I arranged a second look. I already had a few places I liked and knew I woud be happy at, but this was a very well respected institution in a place I'd have liked to live, so I felt it would be good to take another look.
After I ended up matching there, one of my faculty members who knows my new chairman was speaking to him about me, and the Chairman specifically stated that the fact that I bothered to fly back to do a second look was looked favorably upon. Incidentally, a faculty member I only met on my second look was also apparently one of my strongest advocates during the rank list meeting. Maybe I would have ended up there anyway and maybe not, but in a residency program that tends not to go very deep in their rank list, being pushed up a spot or two may make all the difference in the world.
So, my advice is that although I do think it is specialty and program-specific, I do think a second look can influence your position. Still, I only think you should do a second look if you honestly, genuinely feel that another day to see how a place runs will help you differentiate programs when it comes rank list time.
