We have a winner!
Pat Gorman, even if you discount the number of times he's been an extra, has got credits for playing fifteen different people in the original series.
Nobody can beat that, surely?
As to the "Did anyone notice...?" question in the thread title, it's worth mentioning that the Doctor has noticed this sort of thing going on.
In The Daleks' Masterplan the First Doctor spots someone in a contemporary police station who's played by an actor who also appeared in The Crusade. The Doctor seems to think its the same character he met back in 12th Century Jaffa.
