Not to dissuade people from playing this game again from the beginning, but for people who haven't finished it or don't have time to replay it, couldn't they make the game read your GameCube RE4 save?
(This is also making me wonder why LoZ: Collectors Edition disc saves aren't compatible with VC saves. Or the two GCN discs that had OoT, as well as the VC save. At least I don't thinl they are.) Since it's the same save data, even if they were written differently, couldn't the later release be backwards compatible with the previous version's save? I don't think it would be difficult...
Of course, whatever the requirements are for unlocking extras that weren't in the GameCube version (like Separate Ways and whatever else there might be) might require a replay to unlock anyway.