I think a list of good rare games would be much easier to deal with. Then we could assume anything else is bad.
I mean, look at the ones that are good: DracX (not exactly rare), and ... uh... yeah. Ok, throw Magical Chase in there and maybe Sapphire (although I think it's way overpriced). What's left?
Other rarities:
The TV Show: Controls are kinda stiff in this game. I might have to try it out again since it's been a while.
Fausette Amour: Decent platformer, but nothing spectacular.
Akiyama Jin Math Mystery: Rare because it was one of the last releases. It was also only sold in book stores... just like Circus Lido.
1941: one of the few SGX games and a decent port. Probably the only port of 1941 to a console.
Bazaaru de Gozaaru: Interesting little game. It's kinda like "incredible machines" game where you setup the board in order to guide the monkey to the goal. From the pics it looks like a cute platformer, but it's actually a puzzle game.
I'm sure there's more out there, but those are the only ones that come to mind right now.