Ive been playing single player skirmish all day long. Been also playing with the game settings. My last match I set both grunt strength and gold income to High. I did not spend any money on citadel upgrades. Neither did my AI. Neither did the opposing AI. Not a single upgrade was ever purchased at any time. I reached level 20, most of the AIs reached about level 15, and no upgrades bought. This was a 5 vs 5 match. We drove all the way to their citadel and destroyed it after like 30 minutes of play. Basic grunts were the only npcs on either side attacking.