Maybe 39% (from 1975-2005) isn't enough for you. That's your call. To me, it's a far cry from "stagnation".

As for growth in worker productivity, I seriously doubt it occurred due to actions of minimum wage workers. Are you asserting that a burger flipper flips more burgers now than in 1975?

If we follow Paul Krugman's logic [1], this is not the case. Workers tend to be paid their marginal product. This suggests that if wage gains were distributed more to the top than the bottom, this is because the productivity of high earners increased more than the productivity of low earners.

[1] http://krugman.blogs.nytimes.com/2011/11/22/taxing-job-creat...

Wow, that's 1% growth per year. It should be closer to 2%.

>Over 40 years, you'd hope for a little more than "considerably".

No, actually, that's about the best you can hope for. It goes both directions, unfortunately.