Thanks for the comment! So both Screen.rip and Page.REST are my way of validating the market. I don't expect these API services to be the end product (but rather the building blocks for bigger ideas).
However, APIs do seem to arouse curiosity among people. Lot of the emails I've been getting follows the theme of "I saw your API and was wondering how we can use to solve X". This way I get a more focused set of real problems (and their potential value), rather than I try to hypothesis problem spaces.
PS: Another cool thing about releasing API first is I can start charging people sooner, rather than having to wait till I build a finished product. It helps since I'm bootstrapping.