I beleive some software does actually use these values. Somewhere in the labyrinth at InsanelyMac, i read a post about someone who reinstalled OSX86 with different "About This Mac" values, then some expensive software he owned told him that his computer was not licensed, or something similar.
Anyway for my previous problems - im just about to install 10.5.7 on a completely clean system, with a Vanilla OSX partition and EFI for all the hacks (currently no version specific hacks, only fake plists).