Reviving this thread, I replaced the rear discs on my wife's MK2 in October last year, they were pretty much rusted away and useless, at the same time I fitted steel wheels with winter tyres on them, the steel wheels with wheel trims pretty much enclose the brakes completely, unlike alloys which let all the crap get to the brakes. I have just put the alloys back on and rear discs are squeaky clean. Can also confirm that ride is much harder with 185/55 16inch than it was with higher profile 175/65 15inch nokian winters and noisier as well. it is the second winter the tyres have been on and they are showing very little wear, in fact they seem to be wearing better than the summer tyres.
My conclusions are that if steel wheels had been fitted since car was new the rear discs would have been kept in better condition, that winter tyres can be quieter and wear better than summers, and the 185 16" tyres should never have been fitted to Jazz as they make the ride considerably worse and are much more expensive.