No, you can't buy in to a network. However, you generally aren't going to meet the people you'd meet at a top business school without going yourself.
"Most of all, put yourself in the shoes of your future boss and imagine whom you would rather hire: the candidate who built a profitable business over the course of two years, or the candidate who sat in lectures and reviewed case studies to get a degree?"
HR departments don't care about your profitable business. They care about checking off boxes. If their listing says you need an MBA, no amount of business sense is going to get you past that.
Furthermore, if I want to keep moving up in consulting, I need an MBA. My options are, get an MBA, or somehow manage to bring in another $20-30 million in work next year. Mind you, chances are the sales people will get the credit for those sales and I'll be in the same spot I'm in.
If I want to leave consulting, the only option is an MBA if I want to keep anywhere close to my current salary.
Hell, you could say the same about
any degree. Why do you think Harvard grads generally go so far in life? It's not because of the coursework. A basic college math or chemistry course is generally the same everywhere. It's because you're surrounded by an elite pool of people who you meet and network with. Eventually you'll all take each other much further than you could have gone yourself. That's the way the world works. No amount of coursera or open courseware courses will change it.