Clearly, that is not an easy question to answer.
One way is to simply try to do some type of benchmarking that may be present in other jurisdictions, whether they be domestic or international, to see if similar fees are charged and what those fees may be. That's one way of looking at determining a value-based fee that is, as you say, somewhat intangible in terms of trying to determine how to approach it.
You could look, speaking in very broad conceptual terms, at what the market will bear. Sort of auction-type concepts are used somewhat in government to try to determine a value for a fee that is not otherwise easily determined.
Those are a couple of examples. They are very general in terms of how one can go about that. Obviously this is specific to the particular case you asked about earlier. That question will become even more complicated than it currently is now.