To create "genre" grouped roms, I'd duplicate an existing system (e.g. Arcade), rename it to the "genre" you like, replace system logos and place the roms in a dedicated folders.
Edit runcommand for the different roms accordingly.
Sure there are more clever ways to do that but this is quite easy and quick.
@lilbud, this is exactly what I was looking for, except I'm hoping to find 8-bit and 16-bit era games. Although with waht TMNTturtlguy has mentioned above, HD game logos may not be the direction I want to go after all. Thanks though.
@jdrassa Sweet. I'm in the middle of custom creating my PSP and PSX gamelists and mix images (scraping them has been unsatisfactory, so I'm getting images and data from half a dozen different sources and putting them together). It's time consuming, but once I'm done I'll be able to get back into RetroPie stuff.