Charging tells you a very important thing: if you're adding value. Probably this would prune a lot of fruitless branches from your development tree.

There is a much larger universe of "wouldn't it be neat..." ideas than there are "this would really ad value and people will be begging to pay us..." ideas. Even things that people will pay for because they add value but that are so small a morsel of functionality don't work either- eg: little tiny utilities where people would gladly pay you $1/month to use, and where you could make big money at $1/month given the size of the audience, but are simply not worth the effort to renew on an annual basis for people because $1 a month isn't significant enough in the customers mind to get them to sign up. (EG: a spam filtering service is borderline here, anything less featurful or significant is not going to get many customers, I expect.)