“Are EPC ratings low on other developments, and are they meaningless for Spain?”
Few properties are rating high in my experience. I only know of one property that received an “A” rating, and that was because it was built as an eco-house.
I would not say they are meaningless and they help give an idea of the energy consumption of a property. The problem is they are subjective as it is based on the assumed usage of electricity based on whats in the property and not what a current owner is using. Example, me. My house have 5 A/C units. never use them. Yet I will get a worse rating for having them. If I remove them, I would rate better.
Where the EPCs are of use it where the technician makes recommendations on how to make improvements. Double glazing, blinds, etc…. But I would say most of this is common sense.