At the early stage, how can one tell if an idea is any good?

This, I think, is one of the hardest questions, probably one impossible to respond.Time is the key.

Here is Scott Belsky's recent response:

"Here’s the simple litmus test: Does your community care? Everyone has a “community” of constituents—customers, users, readers, clients, etc. Share your ideas liberally. If your community engages with them (either for or against them), then you know you’re onto something. If they don’t look twice you know that you either need to reconsider the idea or rethink how you communicate it."

From this interview:

http://www.openforum.com/idea-hub/topics/the-world/article/how-to-make-ideas-happen-guy-kawasaki

It's a shame that the interviewer doesn't dig deeper. I'd agree that community is important, but one cannot trust committees. How many ideas would have been dismissed because of short-sighted constituents. Surely community is an element, but there are other details to be considered.