That's the thing: I don't believe they're only for looks.
Porsche or Ferrari wouldn't use them for looks. Look at their history: they've never done something solely for looks.
And while most cross drilled rotors do tend to crack easily, most don't so long as they're drilled properly (i.e. chamfered). Straight drills cause pressure points which crack easily, chamfered spreads the load.
What I'm basically trying to get across is that they're better over a period of hard braking, but they definitely won't decrease your braking distance.