Final question:
How to make AI mines change the balance of a fight in a way that would be interesting for the players to evaluate and test and build through or around?
I think the role of mines should be to strengthen the defense of a system, either through applying damage/effects to the attackers, OR by creating 'terrain'.
If AI mines were mostly visible but not attackable, they'd provide the player with a choice: Face tank a path open, or go around. There might need to add a third, anti-mine unit option (Cleanup drones!) just for those that don't like those paths, or maybe allow AoE attacks to damage the mines. That way warheads, Martyrs, etc, could be used instead if necessary.
Other types could do less damage, but be cloaked. All the other types of mines (EMP, Spider, Reclamation) could be in there for the AI to play with, too.
Imagine some reworked, or new, AI Subcommander types taking advantage of high-damage visible, or cloaked, mines... !fun!
My initial distaste for your infinite-use mines is that decloaking is something difficult for the human player to do. There are not many sources: Decloaker, Tachyon Warheads, Tachyon Microfighters, Tachyon Drones, Scout Starships, hacking. All have very low caps, are fragile, are not standard, or even cost AIP.
On the other hand, it would actually encourage players to do something about the mines in systems they traverse regularly.