I personally find mines to be very useful in SP. The AI is almost as bad at dealing with them as starbases. You lay them out and AIs come smashing (and dying) through. Though yes, you need to do it manually. Never trust the AI in placement of anything.

They can definitely work, and are probably one of the best ways to kill forces that greatly outnumber you without resorting to starbases.  The big problem, especially against the highest difficulty AI's, is that every target that so much as strays nearby these things is going to trigger them, which means you have to be careful to deploy them right before the battle happens otherwise they'll just get depleted before they do anything useful.

I just wish the AI didn't sometimes get trapped in a logical loop where it decided all it can have its drone hosts do is either build homing mine squadrons or lay homing mines. Seems like a terrible waste of squadron slots for homing mines. On the other hand using mines themselves doesn't seem very useful vs upper level AIs for the very reason Darvin3 mentioned.

Makes sense, so after a long enough time the AI (depending on the personality) ends up with only homing mines since as the bombers and fighters get destroyed they tend to be replaced by homing mines which are often not targeted.

You can designate areas and queue movements. I do that constantly with TEC and Vasari mines. It is a bit more difficult with Advent, but if you wait for long enough for the carriers to produce 150 mines you could queue them that way. And yeah, agree with the need for upgradable mines. We use them in Distant Stars ourselves.

As for offensively, No. When it was discovered that you could use them that in the early beta it was fixed so as not to be possible. I have heard there are certain Vasari abilities that can help you attempt this or if you distract the enemy long enough for the activation of the mines occur you can pull it off, but it is difficult.

well it would require that you have about 50 carriers each building the mines at full capacity (3 squads each)

when they are built, you release each and every one to specific locations of your choice