> window-size-change-functions calling code could detect if a window with
 > a buffer-local hook changed its size, and not to call its hook in this
 > case.  This would be even better than using global hook where you can't
 > implement such optimization.

Agreed.

 > window-size-change-functions calling code could call it only once
 > for every frame, even if the same buffer is displayed in multiple
 > windows.

Agreed.

 > I see that it's not called when the buffer is not displayed in any
 > window on the frame - this is correct.  But what I noted earlier is that
 > it's not called when the buffer with the buffer-local hook is not the
 > current-buffer in the selected window (but it's displayed in a
 > non-selected window on the frame) - this should be fixed to call the hook
 > regardless if its window is currently selected or not.

Agreed.  I attach an untested and undocumented patch.  Please have a
look.

martin