Is your opinion biased on the fact that you spam copper warriors primarily until T2 units are available? Not that the strategy doesn't work, but doesn't it seem a bit warped that T0 warriors are viewed as better than T1 units?
As for my specific idea: lets say archers are "fixed" as this thread suggests. You still have to choose between horses, archers, or axes. Inevitably you will be forced to choose one unit type over another, probably not archers. This is a bit boring in my view. With my idea, you don't have to sacrifice choosing between the T1 units, but you do need to create specialized buildings if you want advanced troops.
FYI, I believe that iXPValueDefense specifies the amount of XP granted to the unit defeating the one associated with the XML you're tinkering with. So, changing this value from 4 to 8 will increase the rate at which units defeating archers on defense will gain XP rather than the archers themselves.
I don't mean to intrude, but one detail did catch my eye.
ixpvalueattack and ixpvaluedefense are bounties, not buffs. Or in otherwords, if the Archer has a high ixpvalue ... I get a high reward for killing the archer. But the archer gains nothing from it, it just makes the archer a jucier target.
If you make ixpvaluedefense 8 for archers, then I will try to get the AI to attack me with Archer stacks somehow.
What if archers targeted melee first in combat outside of cities?