How to clean up worn figures?

I'd try hand soap and an old toothbrush in some nice hot water for a start. It worked wonders for an old Food Fighter figure I got on ebay awhile back, and also helped clean up dirt buildup on my R3 tech Big Show not long ago, too.

Yeah, try soapy scrubbing first, at the very least it'll get rid of any actual dirt and g rime. (why the hell is "g.r.i.m.e" a spam word?)

Anything left over is paint marks from crashing into other figures. In that case you can try quick swipes with acetone, works great on limbs but can cause hazing on the hard torso plastic.

Or you can move to fine sandpaper, which is basically what magic erasers are.

Or you can simply gently scrape at the surface with a blade and that usually does the trick. To avoid slicing, make sure the edge points towards you and scrape away from you, or vice versa.

Goo Gone works well as well....

I use Goof Off wipes! They work tremendously