I will also say that this is a great idea, and I'm looking forward to it.
One piece of advice though. Your new graphics rely heavily on dithering for shading. The only games I've seen use this shading technique are the... well... the bad ones. Nintendo never used dithering in any of their games on the NES or Gameboy. The other old-school greats (Megaman, Castlevania, etc.) also avoided dithering. I think your hack would look a lot better if you steered away from that technique too. I'll try to doctor up a screenshot later today as an example.
EDIT: Here's an example of what I mean. It's not the best sprite-work, but it should be enough to illustrate the point.