Your upgrade for the front bushes would be poly bushes from superpro etc plus also an anti lift kit for the rear consoles. IIRC the S3 rear console bushes were solid rubber rather than the voided rubber fitted to GTi however the extra castor as well as stiffness of polybush will help tighten steering as well as giving better traction. That was my experience of the superpro control arm kit and there was no noticeable NVH issues with their road durometer bushes.