Catherine, from your list I would suggest that reused building components are by far the easiest to quantify on a generic basis, as in when you don’t know the specifics of the situation (I agree with Martin that it needs to be looked at on a project-by-project basis). I think that flexibility, adaptability and D4D shouldn’t get any EC credits until something is actually reused, which is the whole point. If nothing changes and the building is eventually knocked down, there is no benefit. It’s similar to the difference between “recycled” and “recyclable”, "composted’ and “compostable” etc. There are other things at play that makes it actually happen, and those are pretty important.
That’s not to say that these approaches don’t matter. It’s just that EC may not be the right metric by which to measure them. Too many what-ifs, Sounds like a great area to study for a Masters or PhD candidate!
A couple of resources to share that are background to what you’re talking about, but won’t help you with the EC question. Forgive me if you’ve already seen them.
Ellen MacArthur Foundation & ARUP Partners - First Steps Toward a Circular Building Environment - The second phase of this report is coming out next week, I believe!
A research poster I completed on Carbon Reduction Potential of Material Reuse - http://carbonleadershipforum.org/download/4198