Also, the computer really needs to learn how to go around defense turrets, and possibly even strike deeper into territory.
I've had AI bypass some planets and attack weaker ones.
Even more so, the comp gets scared of them (10-15 is enough to scare off pretty large fleets)
I've also had AI fleets pound at my fully developed 35 point defenses until it beat them into submission, even with me constantly building new ones. The old AI would run as soon as you knocked out a few capitals, the new AI stays and even brings in reinforcements until it pummels them to death.