What are some games with fun upgrade stacking?
I've been playing Shogun 2 with Radius mod and I recently discovered that the encampment buildings in this mod can be upgraded twice, the second time making it the special resource version (so a hunting lodge > a master bowmaker). So if you get a province with a special resource you can eventually stack like 6 of them. Currently I've got ashigaru with better armor than Naginata Samurai, and because ashigaru are really easy to get at higher experience you can get units with the same stats as samurai approximately for half the price and 3/4 the upkeep. You can just have a province recruiting 4 or 5 Naginata Ashigaru per turn every turn forever and use three armies in every single battle.
So with three armor ones you get +9 armor and 3 weapon +12 melee attack. That's more than the base values for most units.
I'm considering doing a game with matchlock samurai and +120 accuracy.