Cab, I'm using this in modelspace. Neither this (16) or the getvar "viewdir" update with pan or zoom , (nor does target) but calling the camera command will show a new target and new camera.
VIEWDIR System Variable
Stores the viewing direction in the current viewport expressed in UCS coordinates.
This describes the camera point as a 3D offset from the target point.
( The length from zero to the viewdir point=length of camera-target so I'm after the new length)