Good idea to handle the section blocks the same way. I've thought about making the admin pages clearer by showing the helptext only on demand.
Gustav, which blocks are supposed to show without a header? Could there be a reason connected to their task to not hide them?
Your proposal could be realized by introducing a new zone at top of the block content to hold for example a line. A click onto this line would hide the content up to that line. But for the moment I think using the top aerea of the blocks as a handle is more straightforward.