The fact you're making a dedicated Genesis, though, means you have the tech to put proper s-video output into the thing... perhaps another reason to try and shove 32X guts into it and sell as a Neptune.
I can tell the games look better. Just play any of the Genesis compilation discs, Cirtual Console, whatever on s-video, component or better compared to the Genesis itself. However, I don't have the cash to pay to have my system modded or get one of those boxes.