I see "how do I represent" questions as beneficial and more in line with "best practice" type of questions. But it is a very fine line between that and "do this for me."
Conceptual problems are design problems. Not everyone perceives a conceptual question as anything other than brainstorming. So, you get flag. GD.SE is a bit different than other SE sites in this manner. Design is not black and white, right or wrong, when it comes to conceptual issues. I don't think every question regarding a conceptual problem is brainstorming. However, each question has to be taken independently to make that call. There's no blanket guideline which would fit every question in my opinion.
I think, and this is just my perception, it depends greatly on how localized the question may be. If the question is asking about how to represent something which everyone will have to represent at some point or another, there is benefit in the answer. If the question is an off-the-cuff "how should I" then there's no benefit to others.
For example, these closed questions:
How can I symbolize credit? and New generation of Add New icon that has no "+" (Plus) sign are merely trying to solve a conceptual problem. Yes it's brainstorming in a way. But it's brainstorming that will help many, many users.
Then again, these open questions: Alternative symbols to represent Valentine's Day? and How to diagrammatically represent High Value Added are clearly just asking others to do work regarding a specific, localized, project.
In short... I don't think there can be a rigid set of guidelines when it comes to the conceptual questions. Let the community decide what should be closed or not.