Moi aussi. My original impetus for going to business school was the realisation that there was a lot I didn't know about running a business, strategy, marketing, business development, finance, cash flow planning, accounting, cap tables, negotiation and all the other little things that add up to a successful venture. I was a CTO at the time, and I was exposed to all this sort of stuff during interactions with the CEO, COO and other board members.

What I didn't realise until after I'd graduated was that having a better understanding of business would effectively make me a better product manager/designer. When you can combine an understanding of business with an understanding of technology, the whole is greater than the simple sum of its parts.

IMO, you can go a long way by picking up a few basic textbooks for whatever your coding. A basic understanding of terminology is really useful and takes far less time than going to class.

PS: If you have never looked into the topic an MBA has plenty of useful ideas. But, I find the cost / benefit of getting an MBA is a negative indicator.

For me, a lot of the learning came from interactions with my classmates. Instead of just reading (or being taught) the theory, you can discuss most of the subjects with someone who works in that field.