Not only should they be build on promising ideas, but they should result in value creating products for the customers.
Without a good idea, no project will be popular among its users, advertising is by itself, but you need to follow everything, but rather how the project develops and in which direction the team will move
An idea doesn't have users, a product does have users. You can have as many ideas as you want and no users, or you can have one single product and as many users as there potentially are.