Decent pads (M1144/DS2500 or PMu/Endless if you're feeling flushed) will give a very noticeable upgrade over the stock items..
312s with the right pads and fresh fluid can and have been used on track by many, they will cope up to a point just fine

The R32 setup is often underrated, but with good pads, quality discs (OE or Brembo Premiums) and fresh fluid is a very capable setup for less than the cost of replacement rotors alone on say an AP 4 pot kit, if they extra weight bothers you then offset it with S3 bottom arms and use the TTs discs?
Not sure what you mean with the £500 R32 kit using TTrs discs, they are not compatible together..