Since some NPC comments fit in well even with larger groups, would it be possible to give each comment a few attributes?
i.e. Gretel spitting
attribute 1: say while larger groups present (true / false)
attribute 2: say when Galmairians present (i.e Cadomyr NPCs commenting on Galmair)
attribute 3: say when Runewickers present
attribute 4: say when Cadomyrians present
attribute 5: say when Outlaws present
Size of a larger group is a bit hard to tell currently, but maybe its scalable, like: if 5 present, say something every 20 mins, if 10 present, every 25 mins, etc.. (standard time + chars present)
appart from that it might nice if a certain NPC comment triggers the comment of another NPC.
i.e. "i fear Mas" -> "You say it, last one we nearly got squashed..")
i hope that goes into the direction you want?