Hmmm...interesting question...
1943: The Battle of Midway
This was one of my absolute favorite arcade games of all time. However, my recollection was that the NES version was pretty lousy. (In an mostly unrelated note -- well, related because it's yet another lousy NES port -- I have the theme to Ikari Warriors stuck in my head for no apparent reason. That game ate a lot of my quarters as a kid...)
Contra
Hell yeah I'd buy it! The real question is -- how come there hasn't been a Contra game (new or improved remake) for the GBA SP yet?
Ghosts 'n Goblins
I'd be sorely tempted to buy this one, although it's a HARD game.
Kid Icarus
Yup yup. I only played this a few times, but I remember it being a LOT of fun.
Metroid
Why would anyone buy this game when you can unlock it by beating Metroid: Zero Mission? (Which RULES, by the way -- I'm enjoying that game a lot right now.)
The Legend of Zelda
Already bought it, and it's still a great game.