I recall a thread on AA with a product that removes (or reduces) the yellowing on the old consoles (eg. C64 etc)...
I will probably end up buying a new set of plastics but if I find the name of the stuff I'll pass it on.
It was hydrogen peroxide and laundry booster ('Oxy') paste/gel plus UV light which reversed the yellowing in old plastics, in a couple of hours.
Try here for starters:
http://retr0bright.wikispaces.com/
