[Q]

IMHO mines are useful even in the later game because it forces your enemy to build and maintain minesweepers.
This is also my biggest argument against the "armor-mine" modification Geoschmo proposed: minesweeping component are only useful to sweep mines, nothing else. There is your decision how much resources you want to invest to be protected against minefields. Armor however is most useful in (almost) all combat situations and therefore you just end up with an increased importance of armor compared to shields.
I still think one more line in the vehicle.txt file for mines as:
"Probability to be cleared = 100"
would be great and not too difficult to implement.
If the value is lower than 100, some of the otherwise cleared mines will be missed by the minesweeping and will damage your ships.
Then you could make higher mine levels useful.
At the moment I gave small and medium mines in my mod lower cloak levels and therefore they can be detected by higher gravitic sensors. But besides that I don't see any reason to use larger mines now.