the 18" Monzas are diamond cut and the laquered, so white worm only applies to them.
whiteworm, as i understand it, is where there has been damage to the face of the wheel (stone chip, curb rash etc.) and water has gotten under the laquer. it is a pain as good quality refurbishing is difficult if you want an OEM finish. it can, however, be done and there is a lot of guidance on here.
alternatively, just get them painted silver and then you don't have to worry about whiteworm.
none of this applies to 17" wheels as they are just painted.
if you're after an OEM type wheel and are willing to spend in the region of £600 can i point you in the direction of W8 performance. he's a trader on here who's selling 18x8 ET44 BBS VZs, which are basically BBS CHs without "motorsport" written on them. they're very similar to the OEM Edition 30 wheel. i've got a set and i'm over the moon with them.