Maybe its good Rod doesn't know more about some of the history. Leaves openings to re-implement an old scheme but maybe a better way that was possibly killed for the wrong reason.
As I read this post and the responses I thought oh, there is a better way thats a mix of both Hamlet's idea and current.
How about implement in the viewer the option to set unique caches for sims you wish to cache? Maybe a button to perma cache a sim you are standing on?
Everyone has a handful of sims they visit very regularly and it would be wonderful to have a sim separated cache for each one that didn't flush unless requested. That way its on the user to pick what ones they think are that important.
Would definitely want it to be a separate folder from the normal cache as it would be mostly static.