Amar Bhide asks in his new book (excerpt) how we estimate the value of new innovations. he describes a study that asked participants how much would they would pay to kiss the famous person (movie star, musician, athlete) of their choice? Try this for yourself. If is really hard to put a value on things that we have never done.
Part of this problem is directly related to Human Factors. What is the true need that the innovation is addressing? What is the (behavioral) cost of the current method(s) used to accomplish the goal. How much better is the innovation at doing it? How hard will it be to learn? How hard will it be to use? What side effects/interactions will there be?
There are some famous quotes that under- or over-estimate the value of new innovations. "Who would want a computer in their house?" "Subprime mortgages will allow millions of additional people to own homes." (at least until they are foreclosed on :-(.
This is one of the great challenges of HF. First, we need to understand the real needs that users have. Then we need to understand our designs and how they will be used in the real world. Unfortunately, this is so much tougher than it seems.