In this situation server bandwidth was an issue. Using an available CDN with the fall back was what we decided to do. It's not that complicated, from the client check if the object you expect to exist in the library exists, if not load it from your server.
When the server is behind a pipe of limited size. When most of your new visits happen all at once over a short period of time. When you can't rely on a mobile phones cache like a desktop because 90% of your visitors are using one. A CDN is a easy win to off load resources, even if they are small.