Regarding the AI going after shipyards, it does do that but it tends to do that only once it feels it has total supremacy.
The 2.8 AI update will make this one look like a joke.
However, it won't be universally positive because players were kind enough to send saved games and I found how they were getting 40 moves per turn.
The entire pathfinding system was designed around maxing out at around 8 moves per turn. The turn times increase exponentially above 8 moves due to path finding tree searches. But there are a couple of planetary improvements the Arceans have that are just insane which I've nerfed pretty hard.
In the long run, the goal is to keep the moves per turn <10 for the base ships (if you add engines, go ahead).
On the bright side, the AI average ship speed at turn 200 has increased from 3.1 to 7.3. That's > than doubling.