Weighting the candlestick helps keep it from being top heavy and sometimes the material used to fill in the cavity of the base helps to keep the thin metal from becoming distorted during handling. The value of an item depends on it's desirability. Intrinsically the value of a silver item is in the weight of the silver used to make it.
A candlestick that is machine made in the thousands will probably not bring as much money as a completely hand made one having the same weight. Though I have seen the reverse occur when the commercial candlestick is in the right pattern and made by a desirable manufacturer.