I don't think you need to replace the rotors unless they are worn or badly scored. All rotors have a minimum thickness, but I'm not sure what it is for the X3. If it is worn, then you will have a definite ridge along the outer edge. Rotors normally last two sets of brake pads for me.

If you do change them, I'd stick with the OEM ones as they are a good product. As for pads, I just put a set of EBC redstuff pads on my jag and love them. Much better pedal feel. I've also used these on my ZM Coupe with great effect.

It's not that hard to do yourself, and you'd save a small fortune!