This sounds like a recipe for disaster to me without a lot more explanation. Time is the main cost to a provider, so it's very natural that time would also be the driver for billing. "Charging for value" sounds like you're trying to say "fixed price" without actually saying it. I have many, many issues with trying to do fixed price projects of any appreciable size (say, more than 20-40 hours).
What do you mean, precisely, by "charge by the value"?