Saltalamacchia = Kottaras IMHO. I don't see a whole lot that the one can do and the other can't -- except that Kot can handle a knuckler and we don't know that about Saltalamacchia.
Kottaras would be a better backup for Tek in at least one way, though, since Tito can use the fact that Kot bats lefthanded to simultaneously rest Varitek and minimize Varitek's weakness from that side of the plate. With Salty, who switch hits, it would be more obvious that it was being done that way simply because Tek can't hit lefthanded anymore, a huge slap in the face that Tito would be reluctant to make.
Do NOT sell Kottaras and Dusty short. THey are not AAAA catchers. Either one could become a half-decent MLB starter if their offensive numbers translate halfway decently. Certainly both have the power to be a more than adequate major league backup right now.
Not that a catcher often reaches that mark, but Kottaras has shown what would be 30 HR power over a full season of 500 AB's. Brown has also exhibited a great OBP, the best arm of the three catchers, and more than enough power in his own right, and has improved each year he's been in system despite starting each year at a higher level. Both catchers have the ability to be effective at their craft and both could probably play in the majors right now.
I do NOT think that the difference between Saltalamacchia and Kot/Brown is worth the kind of prospects it will take to bring him here. Especially because the Rangers are desperate for pitching and any package would start with Masterson with an eye towards returning him to the rotation.
(for the record, apropos of nothing, the fans at RoyalBoard are dreaming over Kottaras right now since they think he might be an inexpensive solution to the problem of John Buck, who really regressed defensively this year)