I don't think art school is good for everyone, but I think it was good for me. I learned a lot about technical art skills, but also a lot about the business side of illustration and comics.
But you really do get out of it what you put into it. I took extra credits each semester and took internships and did independent study assignments. I made a point of taking classes with teachers who I thought I would benefit from and made a point of actually talking to them. I worked really hard and learned a lot and made connections. It was good for me to get crits and hear other artists's ideas about my work. I definitely would not be the same person if I hadn't gone.
But there are some people from my class who did every assignment like it was torture and hated the teachers and only did the bare minimum. And those are the people who now, 3 years later, don't have any new stuff in their portfolios because they stopped creating art now that there's not a professor on their back with assignments and deadlines. For those people, I would say art school was an expensive waste of time.
I guess you have to really consider what's important to you. I'm much closer to achieving my dreams now than I would be if I had gone to school for something else and kept art as a hobby... so there's that! But I'm also in debt from loans and don't have a lot of free time to spend with friends or do other hobbies... so there's also that.