One comment about part /1/: I agree it is beneficial to limit paying extra credit to active miners first, but I would advise caution on how to classify 'inactive' miners. I use this pool as a backup pool, so my average hashrate is very low, and this pool would become useless to me if there was some arbitrary 'active' MH/s threshold other than '> 0'.

I think the best idea from part 1 is to limit the extra credit rewarded in a round to the amount of normal credit earned, this would automatically reward only active users, without any arbitrary minimums. I think it is also a 'fair' approach in that the rate of extra credit is directly proportional to the rate of active mining.