When I'm approached to join an 'idea', I look for three things. Without these three, the idea has a tough time becoming a product.

Technical expertise: someone needs to be able to build something people want (and ideally will pay for). Things like lean methodology help provide the focus and direction to find this.

Marketing expertise: someone needs to be able to reach your market so they find you and convert.

Money: either you have some, make some with the product, or someone brings it to the table.

These things can be done by 1-3+ people, if they aren't there, I hesitate.

Maybe this is why I like pursuing ideas that make money. I'm open to ideas but they are just that, resource hungry ideas that need money.