Aside from graphics and cutscenes with voiceovers, the only difference between RE: Chain of Memories and the original GBA game is that one of the cutscenes in the original game is now a full boss fight. I'll just let my younger brother buy this version if it is released, since I already have the GBA version.
Side note regarding the KH games already out in the US: It's weird that the two console games have difficulty settings, but the GBA game doesn't let you choose - you're stuck on expert mode the whole time. I don't know if RE: has difficulty settings or not, but if it does, I'll play on the hardest one anyway, as I have with every other game in the series.
I too am looking forward to 358/2 Days, if only because I want to get in on some of that 4-player Wi-Fi co-op action (ditto for the new version of Gauntlet).