Lots of good inputs on this, but one more consideration:  The term
"maneuvering speed" has historically (and legally) designated the maximum
speed at which the controls could be moved to their stops without structural
damage.  The assumption could be made that the wing could be stalled during
this event so wing strength is a criteria.  Another is that all of the other
structural elements in the aircraft, such as the engine mount, have been
designed to have equivalent strength.  If the G loading is a fixed 3.8 G's
for example, it will be achieved at 1.95 times the stall speed, which in
turn varies as the square root of the weight.  However, this is not the only
structural consideration.  Stress in the spar will go up directly
proportional to the weight.  Loading on the control surface will go up as
the square of the speed.  What about the torsional moment in the wing caused
by aileron deflection?  That also goes up as the square of the speed.
Negative elevator deflection may not be sufficient to stall the wing so
negative G loads will go up as the square of the speed.  Another
consideration:  The FAA definition assumes the controls are deflected from
stabilized flight, not back and forth from full stops, only in one direction
from neutral.  This is especially true of the rudder and some aircraft have
been shown to break if the controls are moved from a full stop in one
direction to the full stop in the other.

Just to assume that wing spar strength is the only limiting factor in gross
weight and in the determination of maneuvering speed or maximum normal
operating speed seems to be a gross simplification (pun intended).

Gary Casey