Totally agree with you, Bunker re-target time is WAY too slow, in the time it takes the Bunker to re-target a gunner has half destroyed a collector. It needs to be cut in half, they already have a terrible firing area, the least they can do is re-target quicker.
No, it means you strategically place your mines to draw much a away from resources and in to the line of fire of your defenses...
I feel like I have to rearm my mines. I don't keep them armed for their damage. I keep them armed because their draw on juggs is a major part of my base design. There is no good reason for them to cost so much.