While they do a lot of MARS IV training, it just one small part of what they do. With the advent of the new ORCA's, some of the heavy MARS training will be done by these platforms and give the MCDV's a well deserved break, that was relayed to me by VENTURE staff,now of course that could changed. Your right that they are not well suited for the mechanical minesweeping role, but the platform is pretty versatile and the Navy is finding more and more different things for the ships to do. As for mission fits they have 3 types of route survey fits, BOIV, DSIS, Rapid Environmental Assessment and not to mention diving, Phantom ROV and SUBSMASH loadouts. For what is costs to put a frigate to sea vice what it costs to put a MCDV to sea, the ships are very cost effective.
As for what real military role the MCDV's fill, the ships do go to Europe and take part in NATO exercises and take part in many things a operational frigate does. I agree with you that we need a litoral support capability and the MCDV's were never meant for that. They are not going ahead with the midlife modernization of the class, and nor are they going to extend the hull. I would say that the ships have another 10 years in them and the reserves will receive a new hull of a larger type of ship, probally a corvette class.