Do you still want to get rid of your R4 case?Most of the improvements were geared toward cooling; slotted fan mounts, more places to mount huge water-cooling radiators, a more modular system for adding/removing fan hole cover plates etc. The front panel now has reversible hinges, and an integrated 3-step fan controller. If you're not going to have fans or water loop radiators everywhere, there aren't any major changes. Some insight here.
Mine is in good-great condition, and still has the front panel protective plastic. Where are you located? I'll have to check on shipping options for pricing.