I could believe that sine-wave does increase punching power a bit; it is similar in concept to the kenpo principle "marriage of gravity", which uses downward motion to add weight to some strikes. The problem I saw was the giant "tell" caused by the up/down movement, which most experienced fighters would be able to see and avoid long before the strike landed.

0.16% is not enough of a power addition to warrant taking the risk, IMHO. I'm sure that it isn't meant to be applied like the way I saw it, and saw many things mis-applied in kenpo, too. I have also worked with some truly awesome TKD folk in sparring, too.
"In case you ever wondered what it's like to be knocked out, it's like waking up from a nightmare only to discover it wasn't a dream." -Forrest Griffin