The nice thing about YC is that you're not investing your cash, but equity. If you have the right business/team/timing/execution, then the cost of equity will be high, but you'll do better than you ever expected so it's all good. And if you don't do well, then your equity wasn't worth much to start with, and you essentially got the HBS experience for free without any of the debt.
Once you go through YC once, you have access to all the information and alumni community in perpetuity (via Bookface). I think it's natural to want to go through YC again as a form of reciprocation (for all the value you received the first time), but you might find that the value-maximizing route is to take capital from other sources if you go to bat again.
Sure, there are things that you get frustrated at (like some 20 year old telling you, at 40, how to do finance, when you would rather be building) but it sounds like the biggest thing is the culture and being prepared to delegate a lot of what you think you know to the way YC tell you to do it. I think a lot of Entrepreneur types don't like being told that their way is not correct!