From: Washington D.C.
Minesweeping is not boring! Minesweeping is terrifying!
I like your scenario and I think you have the right general idea; one doesn't clear mines just for the sake of clearing them. Usually, one is trying to get a group of ships from one place to the other. Mines aren't usually employed just by themselves, but rather as a combined threat that might also include submarines, surface ships and aircraft employing cruise missiles, bombs, guns, torpedoes, rockets and missiles. So the focus of the scenario for the player's side ought to be three things:
-Delivering the group of ships to the designated area.
-Protecting the ships along the way
-Protecting the minesweepers
I would cut out the "decoration" and look at just the attacks on the minesweepers, the ships they're trying to clear a route for, and the things protecting the minesweepers. You might also consider focusing on just one port before adding more.
From the computer controlled side, I think you need to focus on why they mined the ports in the first place, and how mines function as one piece of a broader tactical concept they're employing to accomplish their goal.