I have had my Diamond Cut wheels replaced once already under warranty and they are beginning to again show wear around the centre boss.

Any thoughts on a suitable non Diamond Cut cost effective 18" replacements which look the part?

Presume I will have to advise my insurance company.

The wheels and tyre on my Superb L & K have been the main bug bear on the car which is otherwise great.

Not much help but I went through three sets during my five year warranty and this last set, although the same effect has started from the centre hub (always the centre hub) have now lasted three and 1/2 years.

If you're out of warranty just get them powder coated. Cheaper than a new set of wheels. If 

Interesting suggestion re Powder Coating.

Isnt that a fairly expensive process?

I got my Themistos done recently by a local guy here for €70 a wheel. Smartened them up no end!