I'm not as high on Mazza as many are. While he was one of the best of the minor league pitching staf last eyar, the competition was not exactly daunting. Mazza strikes me as another Walden, a player who made a good first impression he will probably never be able to repeat. I would be far more surprised if he were able to maintain even his moderate success than if he were to just pitch his way off the roster.
I probably have more faith in Springs than Mazza. While Mazza has had the better MLB career, we are talking about 46 innings. Comparatively, Springs was actually better in the minors, which could mean over the long haul, might actually be better in the majors. He's also three years younger.
But no one on that list is irreplaceable, and finding the next one season flash in the pan is not that hard if you bring in enough candidates...