The main themes are:
Greed is certainly a recurring theme as this is what motivated Midas to make his wish in the first place.
The damaging effects are portrayed throughout with both husband and wife, in the end, being left alone to suffer the effects of wishing to possess a substance which ultimately feeds no one.
Consequences are dealt with as we observe the impact of the gift on Midas and his wife. Duffy invites us to consider how something so precious like gold can easily become destructive.
Isolation and loneliness in the end is all that is left for either character.