With so many negatives and "not"s in your question, it's hard to be sure whether you are asking:
(1) Given you are playing Stash/Chancellor, when would you buy Border Villages with 6? or
(2) Given you are playing Stash/Chancellor, when would you NOT buy Border Village with 6?
My reply and perspective is that the answer to (1) is "under special circumstances only" and (2) is "nearly always". In other words, my default rule when playing Stash/Chancellor is not to buy Border Village. (It doesn't really help you, so why bother?)
Cards that would make me WANT to buy Border Village: Pirate Ship, if my opponent is running them
Cards that would make me NOT WANT to buy Border Village: Tournament (I want to hold Provinces in my hand to deny your Tournament, not draw my Provinces from Border Village), Young Witch (again if Chancellor is the bane I want to hold the Chancellor, not draw Chancellor from my Border Village).
In a Chancellor/Stash deck the Village is effectively +1 Action +1 Card (since you need play only one action per turn), so the question is more or less equivalent to "when do you want to pad a deck with cantrips?"