I don't believe any idea is wholly worthless. Great ideas are on time, good ideas only feel late, and bad ideas are simply too early. For years I've kept two folders.

One I fill with concepts (if they can be called that) I plan to test, and the other is for those I think are too early. The good ideas have kept me afloat; the bad ideas however, have led to great things.

Always write it down. Circling ideas are an omen you're mastering the science but not the art.