Like the Home/Professional/Ultimate licensing tiers of old, each presenting slightly more features than the last? Or more like in-app purchases on mobile phones, providing additional features for increments of cash, proverbially nickel-and-diming the user into oblivion?
Both of these things have been done, and of course, their worth is in the eyes of those making the money.
not exactly. More like you offer a base line service (for example sake lets say for free), then you offer individual feature add-ons at a cost. That way, rather then paying x$ for upgrading say, professional to ultimate and getting a bunch of features you don't need, and the single one that you do, you buy exactly what you want, and no more. Also could provide a way of priming your users to submit features that they would actually want to pay for.
Both of these things have been done, and of course, their worth is in the eyes of those making the money.