Sorry, in retrospect that first comment came across as super condescending when I didn't mean it that way at all.
How do mandatory pre-reqs fit into this?
I agree with you here -- they suck and shouldn't exist. I had the luxury of attending a school that (with the strange exception of the Econ department) didn't allow mandatory pre-reqs as a matter of policy.
You want to know what kills the desire to seek harder things? When you have to complete a mountain of tedious bullshit that you largely already know to get anywhere, and there is no getting around it.
Sure. But that doesn't mean that the opportunities for hard things aren't there, just that you weren't motivated (and perhaps rightly so) to pursue them. Also, these things are only tedious because you already know them. It sounds like you went back to college because you saw an economic advantage in doing so and are upset because it wasn't also intellectually advantageous. In other words, you were optimizing for economics and not knowledge. If you were instead optimizing for knowledge, then it sounds like going back to college would not have been the best choice for you, although I still stand by the claim that it's impossible to go through college without being presented with an opportunity to learn something of deep and meaningful value.
Anyway, I think the problem is not so much that college is generally useless, but rather that there is an economic benefit for seemingly smart, self-educated people like yourself to go back to college even though the experience is perhaps not that useful for you otherwise.
EDIT:
My point is this: Just because you can pass classes you already know everything about with an easy A in college doesn't mean that there isn't an opportunity to learn more advanced things via the faculty and resources provided to you and it's partially on you to take advantage of those opportunities. Moreover, I think it's impossible to go through college and have none of those opportunities open to you.
With that being said, college isn't necessarily the best way to learn things, and whether or not it is is completely dependent on who you are. In your case, college was probably economically advantageous in the long run, but sounds like it wasn't the best way to learn novel skills. This doesn't mean college isn't a valid way for people to educate themselves generally, as not everyone comes to college able to place out of everything.