If someone plans to set up his/her own shop some day definitely, then is does it make sense for him/her to attend graduate school just so that he/she may have an awesome social network? Considering the hefty student loans that need to be repayed asap that accompany graduation....
Given the previous answers, I had to add my view. In my own case, I did an MBA late in life (I'd just turned 50). Now I teach part of the MBA programme at a management college.
Yes networking is a part of it, and I'm happy to introduce my students into my own network. But so too is the learning. Maybe the college where I work is unusual, but we put a big emphasis on entrepreneurial skills as a part of the MBA programme.
So it sort of depends on what you know now. If you need a thorough grounding in business, go get a Masters. Remember it doesn't have to be an MBA. An MSc in Management will cover much of the same ground, faster, and therefore at lower cost.
Mike