How close are these green ones (XBOX 360) from US Plastics to the OEM counterparts? Can you post a side-by-side image of them for reference if you have time? Good to know about the Wii, I have a crap ton of shit cases for the Wii that were games I bought used at GameStop and a bookstore.
The 360 cases are close enough that I can't actually post that picture for you... looking at them now, I genuinely no longer remember which ones I swapped & I can't tell the difference enough to pick them out again... I think it's a group that are a tiny bit more translucent when viewed from the edge, & have a texture when touched... but those are also all Guitar Hero titles, so I don't know if it's an Activision thing or if I just really messed up my Guitar Hero cases back in the day. (Did Activision use eco-cases? I know I replaced all the eco-cases.)
Also- it's not a permanent solution, but using furniture polish can help shine up a shelfworn case, so some of your less egregious examples might be salvageable. Plus, a good foaming lemon polish is a handy mild sticker remover, when you don't want to scuff things up worse getting gunk off.