Jimbob:
The extra-mines trick you mentioned has been fixed with the latest patch don't count on it for much longer
Mine warheads can also be given the fancier damage types.
Null space, engines-only, weapons only, and shield generators only types of damage all work the way you'd expect.
Armor-skipping is essentially the same as null space, since shields are not a factor vs mines.
Also, Shields-only warheads are useless, since shields are not used.