almost never, mainly because I never finish games either! after a while, once you've fought your way out of your starting position and conquered quite a lot of land, most factions become very similar and I get bored.
I was the same with STW, got bored once about half the map was mine.
I've beaten VI on partial victory a couple of times. Usually play on Hard, GA... rarely get past 1270ish cos I always start a new game and the old one rots away in the SaveGame section until I look at it again, decide I can't remmeber what I was doing and delete it...!