I totally agree: the ranting is just for brainstorming - you might be surprised how many good points can come out of a heated rant/discussion. Sit yourself down with someone you know you can argue with, and see what you argue about passionately.
Alternately, write a page on your current idea. If you can't get a page of decent points, you need more research. If you can't bring yourself to write a page on your idea, it's not something you're all that interested in. Ditch it, and find something else.
Actually, there are about 50 billion things you can do to brainstorm and so on, I never even used the ones I've said above, but I reckon they'd work. (I find myself getting worked up over the most mundane things, cos they're close to my heart.)