I wasn't one of the chosen few that got to read book 3, so everything I say would just be speculation at best. However, since I don't want to give anything away to those that haven't finished book 2 and we don't have an invisible text color that only shows when you highlight, I will keep my comments to a minimum.
First off, I thought Gold showed you glimpses of yourself had you made different choices. This is pretty much useless because it is like dwelling on the past. However, Vin may use it in conjunction with malatium in book 3 to see how she and those around her might have been different had she made a different choice at the end of book 2.
Second, I highly doubt that the voices in Zane's head are afterthoughts. Vin's mother heard voices too and it seems to be an integral part of the story so I doubt this is the last we will hear of it. Perhaps they both heard the same speaker, almost 10+ years apart.
To further throw stuff against the wall to see what sticks, perhaps this voice told Vin's mother to perform a ritual on one of her daughters involving a gold earring and the death of her other daughter, somewhat similar to the creation of an inquisitor. If they were the same voice, the speaker might have turned Vin into what she was and did not want her to be killed by Zane.