The mine thing is definitely improved, and the AI is better in many ways compared to pre-Gold. It's still not too hard to find ways to beat it, but it is much improved. I think the first area you mention has been tweaked, too, but I don't remember seeing that specific problem before.
There is no big problem with minefields anymore. Several TDM AIs are in fact can zip through yourminefields As to focusing on one particular planet - that still can be seen. It is a computer after all, not living being. If you feed it with the same input data, you will get the same output every time. I don't think it is something SE specific
It is forbidden to kill; therefore all murderers are punished unless they kill in large numbers and to the sound of trumpets. - Voltaire