Another thing that I forgot about was destabilisation.
In the AW game I played I was hit hard by destabilisation (I assume by more than one AI). When this happens it's almost impossible to get out of, since the only way to raise happiness is to lower taxes/build buildings (which costs a lot of time). If you lose control of the Senate, it's game over. Hitpoints go down on all your ships, and you usually lose stats in another vital area (especially painful if you lose it to the populists).