Yeah, if you get a slot1 for DS stuff and just use the Supercard for GBA stuff, you'll have your very own "pocket arcade" full of games from both the DS and GBA.
Between retail games and homebrew and emus across my CycloDS, and M3 Perfect, or Supercard MiniSD, or EZFlash IV (I have all 3), I have 700+ games (I'm gonna have to actually count them one day) at my fingertips in one handheld unit. 2gigs holds a lot of GBA stuff, couple that with my 16gig in the CycloDS and.....well.....game on!
I couldn't imagine just having a 3in1 for slot2, it had to be a dedicated cart like M3 Perfect, Supercard or EZFlash IV that I could load up with hundreds of games. And that's what I did. Being a person like me who bounces around from game to game, it's the best way to go.
There also the ability to dump DS games faster than the WiFi method if you have a slot2. So that's great too.