I think that, after looking more closely still (too closely probably), regenerating dynamic but unchanged content can be avoided as long as 1) we limit the calls to Provider::process() to only the places where the Provider is known to need to provide new content (e.g. where everything is not already cached, including matching styles and so on). and 2) the given Provider's key() method doesn't depend on the full content generation cycle to happen just to get an appropriate unique value to return.
Given that, Provider-level caching may be a solution in search of a problem.
It's in search of documentation so that new users don't have to dig as deep into it as you did :)
--r
