Decadence suggests a fall from grace or a debasement of the natural laws. It describes self-indulgence rather than a concern for global matters.
Psychological / emotional perspective: Decadence suggests self interest and a profligate use of the resources we have.
If we are content with the sense of decadence in a dream scenario we are learning to value ourselves better.
If it distresses us then we need to assess how far and how much we are moving away from our own sense of self.
Material aspects: As poverty becomes more of a global issue, we become more conscious of the differences between lifestyles and just how decadent, materialistic and wasteful those who have enough can be. When this is highlighted in dreams, we would do well to pay attention to such matters in everyday life.