Even for someone who doesn't push their stock brakes to the point of fade, the bigger brakes are probably going to be more responsive and immediate. The stock brakes are kind of like "are they working? Oh, THERE they are.." (exxagurated of course).
The pedal feel should improve w/ bigger brakes. And pedal feel is important. If you ever read C&D or Motor Trend, for instance, they will always bitch about soggy pedal feel.
You're correct about the adhesion of tires being the limiting factor in deceleration, but there are other useful benefits to having big brakes.