I've been told that mineral spirits will remove 
the "dusty" look from cels. I have not tried this 
since mineral spirits are also very dangerous to 
the paint. . . and strike me as something much 
harder to control as a cleaner (not to mention 
something very difficult to remove from the cel 
once you're done cleaning it). I also don't know 
anyone directly who has tried mineral spirits.

I can say I have a Cutey Honey cel with a lot of 
those annoying white spots, and I have tried the 
following to remove them:

water alone
rubbing alcohol
soap and water

The water and/or soap and water did nothing. The 
rubbing alcohol seemed to reduce the "dusty" 
spots, but wouldn't remove them completely - and 
they seemed to come back after a couple of months.

I really don't think there's anything to be done 
about them. . . ~_~  But if you try the mineral 
spirits and they work, let me know. . . I'd love 
to hear a first hand account of the effectiveness 
of that method. . .

Many Sharp Smiles,
--Drac