I'm in the same boat of trying to come up with something useful. It's one thing to have an idea and another to commit to it. I suffer from the latter. Per Leo, I need to say no to many other things that interest me and stick to one. It has been tough to do so but fortunately I know what my problem is.
One more thing, most if not all of my ideas came from tinkering on how to solve big problems or needs.
Best of luck.