So, 2 things from what I read
1) Silver was always better, but gold sucked so much they had to sacrifice a silver to get them to be remotely useful
2) Power is lost in sacrifices. It doesn't just fail to transfer, but leaves the family entirely. This power lost is kept by the spirit of the sacrificed. Over several hundred generations, this power, the number of vengeful spirits, built up to be practically 100% of the families power.
So, in short, they screwed themselves over. I wonder if the other families who have weakened powers (compared to Salvatore) did similar things.