True enough I guess, but I am pretty sure he has only one year left on his contract. I doubt he will get another one, so think it might be worth hanging onto him.
As I said before, Skrtel and Agger would be first choice, neither of them are exactly old, so buying another centre back who will want to be playing all the time won't really work. Agger is still pretty unreliable, so that is enough to give Coates enough matches next season, and then we have Carra available to fill in where required if necessary.
If it turns out that he is not getting games, or if another young player emerges and looks good then fine, its probably only for a year anyway. If we actively tried to sell him at the end of the season then chances are we would end up paying off a chunk of his wages anyway