I have no experience of trying to drill a disk, I suspect its not worth the effort. Unless there is something wrong with your front brake its more than adequate for the weight of an MZ. In theory I suppose it might clear quicker in the rain but I have never noticed any particular delay with mine – unlike some of the early Japanese s/s disks which needed a full revolution before anything happened.
Regarding s/s spokes it depends on what yuu are comparing them with and where you get them from. The MZ chromed spokes will always eventually rust, s/s ones never rust. If you buy from certain German sources, the s/s spokes are actually cheaper than the chrome ones- around £28 a set.
try http://www.meinzweirad.de/ you will need google translate then look in the section called ‘Landing Gear’. Be aware that postage is quite high but is the same however much you buy so stock up with other goodies as well or do what I do and buy for your mates as well to share the postage.