However, the Va does vary with weight...the basic premise is that at or below this speed the control surface "unloads" (stalls) before deformation an'/or structural failure occurs.
I'd have to disagree with you on that one. Va is a single declared speed, used to ensure that the control surfaces are not subject to excessive loads. I am familar with the wording of the FAA "Pilot's handbook of Aeronautical Knowledge", but the intent of the FAR regulations and the associated advisory circulars is clear - it is assumed that even if the pilot imposes maximum control deflection at Va, he or she will check the manoeuvre before the aircraft G limit is reached.
Vo was added to the Standards to address introduce a speed closer to the classic understanding of Va.
With regards the Airbus rudder issue, IIRC the design case for the fin includes that of a sudden displacement to maximum, followed by a return to
neutral. In the case of the AA accident, the rudder was (repeatedly?) moved from stop to stop.