I think there is a science of intelligence which (in my opinion) is closely related to computation, biology, and production functions (in the economic sense).

Interesting that you're taking into account the economic angle. Is it related to Eric Baum's ideas (e.g. "Manifesto for an evolutionary economics of intelligence")?

The difficulty is that there is much debate as to what constitutes intelligence: there aren't any easily definable results in the field of intelligence nor are there clear definitions.

Right, so in Kuhnian terms, AI is in a pre-paradigm phase where there is no consensus on definitions or frameworks, and so normal science cannot occur. That implies to me that people should spend much more time thinking about candidate paradigms and conceptual frameworks, and less time doing technical research that is unattached to any paradigm (or attached to a candidate paradigm that is obviously flawed).