Agreed. When there is something to show, then make a video. Otherwise, the weekly updates should be more than enough!
If anything, I think doing too many videos can be just as negative as not having any. It takes away some of the imagination and anticipation - the same way that film trailers can spoil the plot too much.
By all means, demonstrate key aspects of gameplay, even doing example playthroughs, but just enough to tease and make people want to play the game!
A key part of any videos should be the quality of the seamless transitions. It's still your USP!