Brian Trelstad and his team at Acumen have had great success using a metric they call BACO (the best alternative charitable option). They can compare the results of the development and investment work they do to the results that direct aid or charity would generate instead. In short: when you understand the alternative, it's far easier to not only measure your work, but value it.
If you are familiar with a great restaurant just down the street, that raises the bar for a new restaurant to get your business…
If you live in a one-company town and have but one skill, you don't have a lot of options. The boss tells you what to do and you do it. On the other hand, if you're a world-class Ruby on Rails programmer with a reputation on Stack Overflow, you have plenty of options, and as a result, your boss treats you with more respect… and you can be a lot more choosy about which projects you take on (realizing, of course, that you stake your reputation on everything you do.)
Call it your BAPO… best alternative professional option. It changes your posture when you have an option. If you've got another client more interesting or better paying than this one, you can confidently act that way–it raises the bar in the way people treat you. When St. Luke's was the hottest ad agency in the UK, they made the decision not to grow–in order to take a new client, they had to fire an old one. What do you think that did to the behavior of the current clients?
Corporations and organizations brainwashed generations of people to believe that they had no option. Go to school, go to the placement office, get a job, do what you're told. The amazing reality of our time is this is no longer true. And yet. And yet few people are developing their alternative, building an external reputation and yes, even moonlighting on the weekends. When you have the option, not only does your confidence change, your work does as well.