By "crowns" I think you mean the spring clip? Their purpase to to prevent the pads from moving around in the saddle (pad slots) creating pad noise. Normally you should replace these 'springs" with every pad replacement.
Btw... I decided to go with BMW Performance drilled and sloted rotors and BMW pads. Once I heard the new(er) pads (after Sept/'10 production) produce less noise and dust - I was sold. I really like the initial pad "bite" when cold. And they do a great job of high speed braking. No noises and not so bad dusting. I really thought the sloted rotors would swiss chease my new pads. But they work well. I do notice the brakes work alot better in the rain or after washing my car! lol
Btw... BMW says the drilled rotors save 2lbs per rotor. I find that hard to believe but... ?