It's only for orc that non-warriors will be ambushed. Because orc elites have a 4/1 offense to defense ratio, you only need to send 1/4 of his offense to get half your land back. That's more than worth it.
Ummm....they don't defend at 100% me, but at 80, so you are closer to 1/5 of their offense than 1/4.

btw, are you allowed to ambush each player who attacked you or just the last?
You can ambush all ambushable attacks on you, as long as you got generals to do it. If someone 4x you, you can ambush him 4x (last first, then second last...). You can ambush attacks from different attackers, but always start ambushing the last attack from the attacker you choose to ambush.

Of course DEs would go all elites and no def specs in that case.
DE should go all elites and no defspecs. It's more space efficient. But, it's a pain cause then they'd have to use offense to kill dragons, and their elites worse at attacking than their offense is (obviously).

during which you can use that +30% spell strength and invisibility to blast him with ops.
Spell strenght will not help you unless you got good enough wpa to break him. (A fail is a fail)

for orcs: warrior>WH