The main thing i want to know is if this game uses the gbalink function.
If you finished Golden Sun 1 and saved it right at the end you get a "complete" save which could then be transferred to Golden Sun 2 (by linking up 2 gba) allowing you to carry over all the djinns gold and items into Golden Sun 2.
I wonder if you have Golden Sun 2 with a complete save in Slot-2 while booting the DS game, if will it unlock or give you something something special. I fucking hope so.
I'm sure those who finished the GBA games are thinking the same thing so let us know if you find out
After thinking about it for a bit, I think it's not possible, because, as kesadisan said, that would discriminate DSi users (and these days, there are quite a lot), and because I wouldn't know what you would be able to transfer. The money, perhaps, but the Djinns would be too many.
Maybe something can be unlocked if both games are inserted in the DS, but I wouldn't count on it.