First of all, I love the Genesis. It was my second console. Admittedly, I pretty much only got it for the Sonic games. I never thought the games ran bad on it. I wasn't much of a Mario fan when I was younger, so I didn't see the point in a SNES. Also, I didn't really get into RPGs until high school and I didn't even know about the RPG monopoly the SNES had until that time either.
Second, Mirby, you're playing it on an emulator. Those aren't the true colors of the DS screen. The vibrant color mode in No$GBA is actually a bit closer to the real experience.
Third, size is relative to where the screen is being viewed. The DS is meant to be paid within a personal distance. This means that the size of the screen isn't that big of an issue. I think that the cropped screen is bit more of a concern. It doesn't look like they adjusted the resolution to fit the DS, they only centered it over the screen. I would assume that would cause numerous potential glitches.