The revelation has been called a "scandal," but it hardly rises to that level. Consulting an astrologer might indicate a certain gullibility one doesn't want in high public officials, but it isn't illegal. It was more like a national joke, just the kind of thing Regan was probably trying to inspire by spilling the beans.
Other presidents and first ladies have been said to have consulted the stars, most famously Warren Harding and Mary Tood Lincoln (and a lot of good it did them, too), but the Reagans' admission was the first time the practice was confirmed. It got a lot of attention at the time, and still clings to the former first lady as one of those things people remember about her.