My idea is to identify schools that clearly are numbers school- got GPA, DAT above the cut- got interview, those are pretty straightforward, visiting them probably will not give you much of advantage. Although it never hurts to develop some kind of relationship with school- go to their open house, volunteer at their clinic etc if you live nearby.
Now some schools do care why you choosing their school over others and want to know they are your number one- those are well worth pre planned visits/ usually done off season- Jan- April before you submit your appl/, meeting with adcom member, going over your appl, talking to school alumni etc. Those would be schols that list that only 60% of their evaluation goes to your DAT and GPA, 40% goes to your interview, PS, EC and everything else. Especially if your grades are just slightly below or way above this school matriculating numbers it will help you to stand out. What applicants tend to forget that applying to DS is double sided process- you as an applicant choosing school, but schools also have their TARGET applicant pool.