There was a study done at the University of Limerick a while ago where some black belts from a local ITF club done straight punches against a sensor to measure the force. They done punches with the sine wave and without the sine wave.
They found that on average the punches from the Sine Wave were only something like 0.16% harder than the punches without the Sine Wave. Although this isn't a conclusive study because it was pretty small, it still raises doubts about how effective Sine Wave was about generating power.
I think it might be a case of perceived power vs actual power. I've seen guys in martial arts who tense their muscles before they strike. It makes them feel powerful (perceived power), but in reality it isn't at all helpful for their striking ability (actual power).
I think StuartA wrote a lot about Sine Wave.
"Let your food be your medicine, and your medicine be your food"