When you say "you're more or less paying for the piece of paper" you're taking it for granted (unless you went to a shitty school). As an Autodidact in Mathematics, programming, compsci, and psychology with nothing but a GED; you underestimate the value of rigorous environments.
Learning fast is also not the point. Learning thoroughly is the point. Thorough and rigorous learning is really fucking hard when an Autodidact. University is an environment that allusively inspires rigor. You're surrounded by peers doing the same thing you are; you have access to instructors that are (sometimes) the best in their field; and you have access to facilities (even as an alum!) that are prohibitively expensive for non-matriculating learners.
Autodidacism is hard because you have to hold yourself to extremely high standards, you have to play with your own psychology to control inspiration and perseverance (you aren't accountable to anyone!!). So even if you learn on your own now after college you still will have a number tools at your disposal that you would've had to develop on your own without college.
Yes, I learn far better on my own too, but do not discount the enormous opportunity you had by going through college.