I'd say try the 5 games out on emulator:
1941,
Aldynes,
Battle Ace,
Ghouls and Ghosts,
Granzort
Darius Plus also takes advantage of the Supergrafx hardware if its there but not to a great extent.
I think Aldynes is fantastic and is one of my favorite shooters on the platform. I'm a big fan of GnG and liked Granzort and 1941 quite a bit. I don't personally like them enough to warrant the console purchase for such a limited lineup of games but I can't think of another system where I would nebulously like to purchase 83% of the library.