Hmmm... I think we may be missing something here. What is the purpose of mines, in a game, and not a simulation?
I understand it to be a sort of random threat to opponents, something to limit our ability to just go wherever we want with our massive fleets.
Some of the irritations for people is the "all or nothing" aspect, so random misses would be a good addition. The tendency is for people to go as fast as possible to reach the 100 mine limit, and likewise to reach the 100 mine sweeping limit. This too perfect numbering system for mines could be countered by decaying minefields, but I think it would be cool if that were keyed to total amount there -- i.e. as you approach 100 mines, the decay increases, but you could conceivably have a few more than 100, for a short while. Then the decay falls off, so that a 20 mine field might lose one only every few turns.
Something I'd like to see is mines that have several components that are needed. The mine hull should have no cloaking, and no "magical only hit enemy" sensor. You drop these killer kegs of ball bearings in space, and anything that enters gets hit. You know where you've laid them, so you can avoid them. Any one can see them, so they can avoid them as well. But what if you have to cross that sector? Build sweepers and grit your teeth. My idea here is to return the mine field to a �do not touch� status, instead of �stealth death�.
Later research can give mine cloaking devices, and sensors that allow friendly ships past (gotta add an intel project to allow one of your ships to steal the codes and allow it's safe passage -- wouldn't that be a surprise, Bwa-ha-ha). The ultimate tech would be Von Neumann mines, that would use interstellar material to overcome the mines' decay rate, maybe even create more mines than were originally laid (you can call those self-replicating mines if you're a diehard Star Trek
S9 fan)
Building on the DS9 angle, races should get angry if normal space lanes are blocked with mines, whereas if you mine a small planet of yours as a defensive measure, people might tolerate that to some degree.