I'm not sure it can ever be quantified, especially when comparing catchers from different teams, staffs, parks, coaching and more.
It's one of those, "You know it when you see it" things.
I liked Vaz, but it was sort of a long-standing beef I had, that our other catchers, for the most part, got better numbers from the same pitchers during the same seasons, more often than not. Even the more unbalanced and smaller sample size comps seemed to greatly favor the "other guy."
Vaz did hit better than the other guy, most seasons and had a decent CS%, and some other metrics, but not that unmeasurable aspect.