If schools offer interviews, you can do that in the summer too. Agree that one can miss the vibe, and that’s important if you’re considering ED, but at many schools we visited, there were quite a few kids who stayed on campus for the summer and who were happy to chat. DS was on his campus one summer, and when friends in admissions ran into people touring who were interested in things he did, they would often connect them. (And his summer on campus didn’t involve admissions.) Everyone just had a bit more time.
Visits are generally helpful but the serendipity of them – who you meet/gives your tour, weather, whether everyone is in the middle of exams, looking forward to or recovering from a big weekend/game – is always there.