One thing I think might REALLY help the AI...

[Repo Man]

I had the same observations. I was getting bored so I decided to take over manual control of a neutral empire which was being attacked by the number 2 empire. My "real" empire gave the neutral several ships, and I build additonal ships for the neutral. I built enough ships to bring the maintenance cost to about 50% of the income. Since the attack never came (suprise suprise) I place the neutral back on AI. Over the next 10 turns it scrapped almost all the new ships.