On most plastics, acetone is very harmful. My kid sister ruined a mini-component stereo of mine a few years back with nail polish remover (w/acetone). She touched the controls and disolved the print on them. Plus made them permanently tacky... Very much like the adhesive on duct tape.
If you did decide to try acetone, I'd test it on the interior of the case before using it as a plastic cleaner/bleach.
[Edit]
It's probably to late for this suggestion as you've already soaked with bleach. But considering how much yellowing you were able to remove before soaking, might you have used powdered cleanser (w/ bleach) and water to make a paste you could apply to just those areas that were still yellow?
