If you ask me, honestly, I think petitioning for a 4th GS game won't be that impactful. If anything, I feel campaigning to spread awareness and build up the fanbase significantly by promoting the franchise via the VC re-releases of the first two GS games would yield better results. Besides, I feel the fact that the first GS game was one of the highest-selling VC GBA games in the first few weeks over in Japan would have better demonstrated that, despite the series being past it's "glory days" the first two games are still fondly remembered by people to the point the series still has enough potential to have a successful 4th game. In other word, considering Camelot was willing to work on a sequel if there was enough fan interest, the VC sales shows fan interest better via money than any petition for a 4th GS game could - a case of actions speaking louder than words.
I think the aim of Operation Golden Sunday should be changed from petitioning for a 4th GS game to spreading awareness of the franchise by promoting and recommending the first two games for people. Because frankly, at this point, if the VC sales doesn't convince Camelot, I don't think anything else will.
As the original GS game was one of the first games showcased and promoted for the VC, I suspect Camelot was using the sales of the game to gauge whether there was enough popularity of the franchise to justify a sequel. Combine with the reason that they have nothing left to do after already making a Mario Tennis and Mario Golf game for the 3DS that they are good at and I suspect it isn't merely a matter of if we'll see a new game, but rather when.
So yeah, Golden Sun does indeed have a future.