I graduated with an EE degree six years ago, but over the years found myself more and more interested in economics. I read textbooks, papers and articles, and over time I thought I knew something about it. It was only when I went back to uni this year to formally study for an economics degree that I realised I knew jack. All the fundamentals and boring little details that I used to gloss over had more signficance than I'd ever thought. I also had access to the university resources, good instruction and a fairly rigorous course structure. Granted I was motivated and keen to learn (sadly unlike the bulk of the 19 year old kids there), but I gained a much more solid basis for understanding econs than I would have had I not gone back to uni.
I'm certainly no apologist for universities and schools, but wanted to point out that there are some issues with self-learning, namely 1) focussing only on the interesting topics and neglecting the fundamentals, 2) unstructured learning can be ill-directed and 3) good instruction is more efficient than finding your own way.