I visited all my programs before I decided to apply. I also visited a couple programs and decided they weren't for me. During my visits, some (probably) didn't increase my chances of acceptance since I didn't interact with any faculty. However, for one school I met one-on-one with a student, another I was one-on-one with a professor. Whether it will help my admissions chances I don't know, but it definitely helped me learn more about the program and if I could see myself attending the program. Another big plus about visiting is that if you are applying to schools outside of your city/state, you can see what life is like in that new location. Definitely visit if you get the chance. It would suck to spend $50+ on an application and go through the awful process waiting to hear back from a school if it turns out you don't like the program and/or location anyway!