I think that for most people with a daily driver any brake upgrade other then better pads is a bit of overkill. (Unless you are a banzai time-attack-style driver on your way to work, of course...
The main reason listed for upgrading the disc itself is to have more mass to help manage heat buildup from track use (or, say, canyon running). The "cost" is that you increase unsprung mass, which can actually degrade some aspects of your handling and acceleration potential.
