The main reason I doubt Marte and Martin is because they both obtain some of their value from walks that they don't have a skill for drawing (not like Martin is a high OBP guy, but he doesn't show the strike zone judgment of a man who should walk 50-60 points, and certainly Marte was never a walk taker before he magically was last year at the big league level).
There are two ways to draw lots of walks in MLB...have a really REALLY good eye for the zone and an approach that is patient and stubborn...or be a power hitter. Marte and Martin are neither of those things. I think SS and CF are going to be catastrophic black holes for the 2016 Mariers and will continue to think that until they prove me wrong.
And FWIW...I've also learned to be skeptical of players with very low BABIPs who are 34 years old or older. I don't think those guys are good bets to bounce back to "career norms" in that regard. So no betting the high side of Iannetta.
I believe I am most likely to be very wrong on the bullpen, Paxton, Walker and Karns (meaning most likely to be underestimating) and most likely to be wrong the other way on King Felix and Cano.