I still think the term "Diplomatic Capital" needs to change, so I'm going to throw a few other possible replacement names based on what others have said: faith, support, clout, allegiance, leverage, etc. Others I've suggested: dominance, legacy, power, sovereignty, prestige (although, already being used).
Like someone else said, DC is too abstract of a concept. We need a better title to fit the concept, IMHO. What is it in reality? What is its simplest, most elegant purpose or model?
You could even call it "ambassadors" which would make sense why you're giving something up for something else!