I agree very much with the idea of "improving on something that already exists". I hate it when you tell someone an idea, and they rule it out because "it already exists". There is always a better way to execute on the same idea.

However, I am not a fan of "Has business model other than advertising". Although it is something to have in the back of your mind, it is hard to say what the product/idea will evolve into when it actually becomes something that can be profitable.