After doing the overnight bleach soak, followed by some scrubbing, here are my findings (sorry, no pics).
-The controller is definitely 'whiter'. Not bright white, but definitely less yellow than before. I can still see where the yellowing originally was, it just looks faded now.
-The bleach definitely seems to wear away at the plastic (maybe this was obvious to everyone but me). My controller was originally in mint condition except for the yellowing, but now, although it's whiter than before, it looks more 'used' so to speak. Some of the thin parts of the controller (like the edges where the two halves meet and the thin parts around the I/II buttons) don't look as nice as they did before.
Summary: I'm betting you'd get similar results with some very fine-grit sanding.