[Q]

Just an idea I am going to try:
Reduce damage of mine warheads to 1/4 = 25/50/75kT for Level I/II/III.
Create mine mount for medium and large mines that increase the warhead damage by 2x repectively 4x.
Increase tech level requirement for medium and large mines to 3 respectively 5.
Increase cost of minesweeping components by factor 4!

Expected results: small mines are quite weak, but because with the new patch their damage stacks not completely ineffective. This might balance the too high power of mines in the early game. For the later game it is important to research and use the larger mines. Minesweeping gets very expensive.