Charging by value isn't simply about setting prices. It's about figuring out how to include items that might not cost you much money but provides extreme value to your customer. As an example, I worked for an organization where I bundled a specific type of graph into their software. Time for me to build: a few hours. Value to the customer: saved thousands of man-hours per year. That's a BIG savings that I could charge a lot for.
The key aspect of value pricing is that you will charge different amounts to different people for the exact same work. Why? The value a given piece of software will create will depend upon who is using it. Want to sell me a system to manage huge amounts of data? I wouldn't even pay a penny for it. Want to sell it to Google? They might spend a hundred million without a second thought.
I think that Sean Wes has a good worksheet for interviewing clients: http://seanwes.com/value-based-pricing/
As a shameless plug, I also wrote a book on how to price software http://TapRun.com/pricing