Love this. However, my biggest issue with prototyping isn't in convincing other devs why it's useful, but (A) convincing clients why they should pay for it, and (B) convincing management why it's a sound internal investment.

two additional reasons i am a big fan of prototyping. First, it's an excellent to store requirements; and second, it's a great way to provoke relentless iteration of the extant requirement list (e.g., some are thrown out, some are refined, etc., the priority order of the entire list might be changed). Giving stakeholders a simple web client with a few widgets that encapsulate the project's technical crux, is perhaps the best and simplest way to encourage their useful feedback, because as they are interacting with the simple prototype client, they are actually thinking about the project in a very critical and useful way.