I'd urge you to remember that you are the professional in the conversation. Clients, especially single-entity type of clients, can be aloof at times and not wholly vested in their conversation with you. They just want art. Some will have a few ideas or visions, others will have nothing to go on. It's up to you to steer the conversation where you need it to go in order to get enough information you need to work. Your the boss. the client doesn't know what they don't know. You do.
A design brief is fairly mandatory. Even if, as DA01 points out, it's a 5 minute conversation. The imperative aspect is that you walk away feeling ready to move forward with a clear understanding of what is expected by the client.
I don't bombard my clients with forms or questionnaires to get the information, I much prefer a conversation, then that conversation may be transposed to contract bullets. (See Here for general questions) I don't take the flippant "I just need something..." responses as final.. I ask questions. If the client gets annoyed by that, then I explain that I need the information to create something effectively. If they are still annoyed.. they aren't serious about the projects and I'll get a contract signed before doing anything (to force them to be serious or walk away).
As for "mood boards" .. meh... never needed one. I may personally play with some "mood" options myself but in the end I will use what solves the design problem the best in my opinion. The client's input on "mood" isn't really needed before I start designing. That's my job to sort out based on the design brief. Sometimes things in the industry are done by other just because "that's how it's done". That's kind of how I see "mood boards". That doesn't mean it's a worthwhile use of my time.