Philip,
   You're right- the ES doesn't "require" an AOA.  It also doesn't require a
GPS, an ILS receiver, an autopilot, a multi function display, or a  whole
host of other things which most builders install.
   Having these things enhances our capabilities and/or awareness.  If you
understood the value of an AOA, you'd have installed one.  Sure your plane
will fly fine without one, but as I've said repeatedly, it's a great tool to
have in your box if you should ever need it.
  On top of giving me stall warnings, if my engine ever fails I'll be flying
my AOA all the way to touchdown, maximizing my available energy in a way
that an airspeed indicator (or even two airspeed indicators like you have)
simply cannot duplicate.
  Skip Slater