I have had my coupe 6 years and recently replaced the rear discs and then bought the front discs as part of the GB. I went out today armed with the how to on replceing disks and pads and was amazed to find that the pads were about 6.5mm thick, minimum 1.5mm and the discs are above the minimum but difficult to accurately measure because of the lip.
I have done 50000km since owning the car so either the pads are very good or I don't brake much!!!
I think I will probably replace the discs and pads as the grooved ones look nice but nevertheless I was still surprised!

Or the rear brake compensator is not working well / at all and there's hardly any braking going on at the rear (but you would have noticed the rusty discs?)

If they are working properly, then after a good drive with plenty of braking the rear discs should get pretty hot, so if they are only luke warm they need attention.

No Dave I am talking about the front brakes!! I have already changed the rears!

If there's a lip that makes measuring difficult, then the discs are ready for replacement

IIRC, new thickness is 28mm, with a minimum of 26mm. This means the maximum lip is 1mm, but you'll probably find that the inside face has worn more than the outside

Thanks Nigel, the manual says min thickness is 24.2 but I am going to change them anyway.