I suppose I’m guilty of conflating dreaming spires and river punts with Anglican dioceses, I just didn’t want prospective students to rock up on an open day disappointed. :)
I think the best "dreaming spire" is the spire of St. Mary's Church, billed as the University Church. There's a spiral staircase up the inside of the spire, made of very worn stone, and a narrow viewing platform around the top, from which you can look down and see the layout of the quads of several of the most-famous colleges. And you can rub noses with a couple of gargoyles.