You also have to consider the discipline, position, and/or industry you work in. For example, my last employer actually discouraged the engineers from getting PE's because the company didn't need them. There was no value to the company for you to have a PE. Additionally, a consultant's career lives and dies with his PE, whereas many construction, government, and utility positions don't need them.
Although you can make the argument that you are worth more because you have a PE, you have to remember that value is subjective. You, personally, may be worth more with the PE, but if you're employer doesn't want/need you to be a PE (or have any corporate gain from you having your license), your license is essentially "worthless" in that regard. You can then gain value with it by applying/transferring to a new/different position (either new company, or new position within the same company) where this value can be recognized.
I know several EE's and a couple ME's who have their license but have it purely because they wanted it. They never got a raise, nor expected one, because the areas they work in don't need the licensure. To them, the license is priceless. To their employer, it's worthless.