UC Productivity Issues
I am surprised that you haven't acknowledged the business productivity perspectives of UC previously described over the last several years. My colleagues at UC Strategies.com have labeled individual user time savings as "UC-U" and business process time savings as "UC-B." The former has been estimated as around a half an hour of time savings a day. But that doesn't really mean much if you can't use that time productively.
On the other hand, what they have labeled as business process productivity or "UC-B," can be extremely valuable, either in generating revenues, reducing costs , or avoiding operational losses. several years ago, I originally used the terms "micro-productivity" for UC-U and "macro-productivity" for UC-B," because the real value is not based on a single individual's time but on the performance of a group of individuals involved in a particular task or business process that has the UC-B payoffs mentioned.
Not all processes have the same UC-B values, so even there the trick is to selectively implement UC capabilities for individual users where the UC-B value is is highest, and that doesn't mean just cost reductions! Line of business management, not IT, must be responsible for identifying those UC-B needs.
Where UC will start generating the most benefits will not be in "person-to-person" communications, but in "process-to-person" contacts, better known as Communications Enabled Business Processes" (CEBP), which will enable an increase in business process automation and minimize the human latency involved with traditional person-to-person contacts.