Keep us posted please, Lynsey - my Charlestons are just shy of two years old (13k) and look perfect - although I knew when I specced them that they were likely to go the way of some Monza 18's, having a similar diamond cut finish.
Reugular washing with Meguiars, dry off with microfibe towel and 3 monthly 3 coat Poorboys is what I've been doing and like you I take a bus to the kerb
My previous March '06 Steel Grey GTI which went to Yan on here still has its original wheels as far as I know and I suspect Yan is as fastidious with them as I was; however there seems to be no hard and fast rule with the worm - other than physical damage to the lacquer?
My car's a keeper and if the worm appears after the warranty expires, I reckon they'd look pretty smart in single colour anthracite?
Good luck on getting yours replaced