I see this new notion of interviewing people before working on an idea is becoming quite popular. I know it's useful to know if people would find something useful, but I think there's the danger of never trying out really innovative ideas. Much like writing, building things is an exploratory process. Typically my own ideas evolve and improve only once I actually start building them. This is especially true for things that are useful to myself and not just other people.
There is the risk that you will waste your time. But doing something new and useful often involves risks. And seemingly silly or bad ideas are often the best - http://paulbuchheit.blogspot.com/2007/06/three-types-of-idea...