I haven't had a chance to play MP just yet, but I thought valour doesn't help missile troops much, unless they are hybrid that you would use in melee as well. The same goes for weapon upgrade. On the other hand, giving the missiles troops a couple of armour upgrades seem to be more useful, since your troops would take a little less casualty from enemy missiles. In SP, I don't notice any difference in speed and fatigue rate between the upgrade and the un-upgrade unit. However, the ones with armour upgrade will take a lot less casualty, especially when they face regular archers.