Interesting Vietnam Balance Idea

I did a quick search before posting this to see where we were with the Vietnam debate and apparently people are generally in agreement a new balance would be useful.

So I've always thought an infantry related buff would be most useful in rounding them out a bit. Half off barracks upgrades is the first idea that comes to mind, but that's very similar to either Bulgarians free militia upgrades or Ethiopians free spear men upgrades. The Ethiopian bonus is envied here because the easy access to spears would balance the focus on archers, just as is the case with Ethiopia. So here is my variant of the spear bonus:

Each age your starting town center produces free spear men. Once you hit Feudal your TC produces 1 free spear man. Once you hit Castle it produces 5 spear men and upon hitting Imp you get 10. Perhaps a special button could exist inside Vietnamese Town Centers that lets you toggle which Town Center will produce the spear men.

Another version of this is one selected Town Center automatically produces spear men for free like, 5 times slower than a barracks produces them.

One more idea: skirmishers and spear men cost half a population space.