Is it OK to ask a question on a Stack Exchange site that could have several different answers (like a brainstorm) or must all questions have a single, correct answer?
I think as a general rule, you should not ask questions that the majority of those answering could not place on a spectrum of correctness: from grossly off the mark, to hypothetically ideal in every way. That is to say if it comes down to style, like what is your favorite color -- you're probably better off not asking it as it will obviously be closed.
Most of the rest is pretension to be honest. There is seldom a best way to do something and most answers -- even the accepted ones -- aren't perfect enough to be outside of the realm of critique by those sufficiently skilled. And, even when the answers is precise and accurate you can have someone like Peter Cordes come in and demolish it by providing a newer answer with more detail, background, and clarity. (that's a compliment, his answers are better than anything any other mortal can do).
"Open ended" means different things to different people. I've been on the site for over 9 years, and my questions still get closed. Some times it's just an out of control close-brigade and not you anyway.