You're failing to consider the alternative no-EnergyStar scenario -- higher aggregate electricity demand, requiring more power plants, so everyone pays more for power.
Either you pay pennies to promote efficiency, or you pay quarters for energy infrastructure.
Not sure this is the elastic droid that paradox is looking for.
Household energy use is not such a good, because most uses have fixed utility.
Very few people are going to cool their house down to 10C because the price of cooling to 15C decreased.
Nor is their overall energy use budget-capped. (Outside of low income AC and/or heating use cases)
Example: as a regulated utility it will often cost more per unit if underused vs optimal generating supply (which has already been passed through into rates)
Additionally, the generating source heavily influences ultimate cost.