Agreed with tel, I changed 6 hoses on my old MKII Golf GTI (4x brakes, 2x rear bias valve - not sure if the A3 has them, I'm sure someone will confirm though!).
The difference was pedal feel being firmer and a little less travel. The process of doing it also makes it easier to renew the brake fluid but the only negative side of it is you can't clamp the hoses up if you remove any of the calipers in future or you will end up damaging the line. Use the plastic end caps that come with the hoses, I found that out after I had chucked them away...