I generally view the campus visits to be more about evaluating "fit" than about obtaining substantive information. It is a great opportunity to look at the physical plant, sit in on a class, have spontaneous conversations with students, check out the availability of housing and parking, etc. By the time you arrive for the visit you should be familar with all of the basic information about the school. If you have a truly unusual background you could use this as a chance to get answers in person. However, I would generally prefer to have the answer to a vital question in writing (both to review the answer at your leisure and as a form of proof).