Throwing in a reply to SignofZeta,
The US TG-16 library is a bit different, as those titles are in english, while most of the jap releases of the same title are only in jap, possily some english here and there. Also, I only know of 2 US titles that fetch over $150. Neo Geo, all the carts are pretty much the same (Except for pin differences between aes and mvs).
PC-Engine must be the poor man's Turbo Grafx (in case it goes over some heads, I'M KIDDING).
MVS, AES, I don't care. Aes may be prettier, however MVS gets the job done for me. The Universe Bios helps. If you dump a universe bios into either machine, I think you can play the aes like an mvs, it works that way on my MVS. That's only a $30 or so upgrade. Joe, take a look into a modified bios, if you haven't already. Some fun stuff there.