What do you feel about skipping ui specs and spending time/money on prototypes instead? Doing VERY low-fi wireframes to get to the prototype perhaps. If a picture is worth a thousand words, an interactive picture with state changes, etc, would be worth how much then?
The down-side to prototypes is that they become self-guided. The viewer has to discover the interaction themselves. It’s necessary to “can” them somewhat in order to make them feasible, so the viewer expectation is rarely met. Expecting a prototype to always have a presenter in place is unrealistic. So create a movie that walks the viewer through the prototype.
Check this out:
http://wireframes.linowski.ca/2009/12/protocasting/
You can spend months designing a very pretty phone book. Something with plenty of “thud” factor. I’ve created enough of these that my portfolio weighs more than me. Or, you can create something that looks and feels like it is “alive.” Something that stakeholders, executives, and board members can watch in a few minutes and “get” right away. Something that developers can look at and understand your intent more clearly. You may even be able to recruit some to help you develop the prototype, turning them into advocates of your design.