Thank you for the information. I am a rather large fan of the Golden Sun series myself. I beat the first one, ans as for The Lost Age, I am currently at Magma Rock. Back to the subject though, this is great news. Finally, an official new Golden Sun announcement. The last rumor I heard said it was going to be called Camelot RPG and be for the Wii. It was on IGN, but even there it still said it was a rumor.
As for extra content for veteran Golden Sun players, being for the DS, there are certainly capabilities to do that. I assume it would work similar to games like the GBA and DS Pokemon games. One can connect a GBA Pokemon game cartridge into the DS slot while a DS one is there and just transer old data to unlock new content. Since this will feature new characters though, I doubt anything would simply transfer over, but more likely something would be unlocked inside the game.
That happened with Final Fantasy Tactics Advance for the GBA with Final Fantasy Tactics A2: Grimoire of the Rift for the DS. By insterted the GBA cartridge with the DS cartridge in as well, you unlock the feature to see traps, quite the boon when just starting out.
I would certainly hope we old Golden Sun players would get something for going through the first two. I can't be sure, but I honestly doubt we would get something for getting all the Djinni from both. Toward the end of The Lost Age, those who got them all are already reward with the ultimate summon Iris. I wouldn't think the creators would reward a player twice for the same thing, but that's just a guess, they may just do something new for those who collected them all.
In any case, I certainly look forward to the DS version's release myself and can't wait to play (despite the fact that I have to until 2010 anyway). Later!