There can be many contributing factors or reasons why something increases, or decreases in value, but basically, it is based upon want or needs. If there is a change in wants or needs, there will be a change in what is valued. It is how people decide their value system.
The important thing to remember is that the economy of your present and eternal life is determined by the decisions you make. Bad and good decisions will affect the quality of your life. The question is whether your value system is merely temporal, or eternal.