The DS can't play GB/GBC games so I'd save up for a new GBA SP.
I don't see what I would play on there anymore.
Maybe my bro's old crystal for the lols, or my old, old, pokemon blue file.
I've had the file for as long as I could remember. Pretty sure I got stuck at Silph Co. and had blastoise around 35, venosaur from stadium in like the 30s, machamp around 30, and alakazam around 40. I know I had 5 pokemon, but I can't remember the last.