Disks on road use cars are for aesthetics tbh. unless you drive like a **** i wouldnt bother with changing discs, Pads however can make a difference better friction and with the heavy a4, especially us with quattro i found my originals faded a fair bit, this was mostly due to needing a brake fluid change. this was much better after the fluid was upgraded.
Braided hoses make a good change too much sharper breaks. but for the sake of a few extra quid the ferodos are an amazing pad, not as dusty either and WILL cut m's off your stopping distance. i'd recommend even my grandma got them for the sake of safety.