We visited when the fall colors were just turning. The views from the bascilica were breathtaking. The church interior and even the chapel are quite beautiful. We stayed for a Mass and then visited the gift shop.
One can take the elevator from the gift shop up to the Bascilica, but you have to walk an additional 178 stairs to see the view from the church's towers. I imagine it can get crowded in the tower on a beautiful fall day, but the views from the Bascilica's base are equally good. You can even see the Milwaukee skyline on clear days!!!
I highly recommend a trip up.