I mean, you do learn things; my understanding is that it's sort of a 'survey degree' that gives you a shallow treatment of a lot of different business disciplines. If they would have let me take the MBA without an undergrad, even at a so-so school, I would have done it a few years into my own adventure running a business, and I think it would have helped me. If you have management experience and skills, a MBA even from a not so great school can help. But I think the difference between a MBA from a meh school and a MBA from a top school is overall far greater than the difference between an engineering degree at a meh school and an engineering degree at a top school.
There is some value to the content, even though I totally agree that the contacts are dramatically more valuable than the content if you go to a good school.
Personally, I find that finding management and business content on my own is actually harder than finding Engineering content on my own; management and business training is full of tony robins style confidence men, and it's difficult, for me at least, to sort out what is actually worthwhile. For that matter, just an overview of what sort of professional to hire in what situation would be nice. (For instance, if you are just looking for tax help and don't plan on selling the company, an 'Enrolled Agent' is actually better than a 'CPA' though the two certifications are of similar difficulty; the EA focuses on dealing with the IRS, while the CPA has more of a focus on the accounting you would need if you are selling your company or something.)