why don't you discuss this with some of the social data mining firms. they may have encountered similar problems
and just to add: I think my particular problem is, and that's sort of the selling point, my analysis and reports is not just growth data (which is easy), but my calculations require all of your follower details to work correctly (to provide correct results). Twitter is sending me random follower details, so having a partial set means little reliability (for up to 60 days).
It does occur to me that the OP is effectively trying to replicate large chunks of the twitter datastore & that's going to be very difficult to manage! It's not like twitter themselves were particularly reliably to start with after all.
and regarding replicating, originally that's what I did. I had up to 20M of Twitter's 140M records cached almost - but that probably wasn't cool with them on the long run and i was unable to maintain a database with one table having multiple gigabytes of data.