I don't think Incognito is the right kind of talent or lineman for the Seahawks anyway. Setting aside this Dolphins mess or his past history, he is a mediocre guard on the wrong side of thirty, and used to a system completely unlike what Cable runs. I don't see why we would or should be interested in him.
Martin is still young enough and with a potentially high enough upside (high second round pick a couple years ago) that something might still be salvageable at least on paper.....but I'd apply caveat emptor with him as well.