We found early touring very helpful. While I understand the “inducing stress too early” argument, we found that there was honestly nothing more stress-inducing than trying to squeeze in tours late in junior year (particularly during spring break when half the country is in your tour group) and the summer before senior year when the kids were immersed with summer research programs, jobs, etc. Tying in a tour or two with an existing family vacation was easy to do and much more enjoyable than the “seven schools in seven days” death march (which we also did).
As others have mentioned, demonstrated interest is a thing at many schools, and tours can be an important part of that. And good notes from information gleaned on in-person tours and department-specific information sessions make the “why” essay in the admission application much easier to write.