interesting.
many , if not most of the major foil manufacturers are using anhedral with their front wings.
more than a few resons have been offered for this use, (i.e. yaw stability, reduce wave/surface interaction, reduce rear wing interference) But i dont believe anyone has claimed increased lift efficiency.
i dont really know the true reason.
if increased lift efficiency is desired , the use of winglets is a proven concept.
particularly for wings with finite/reduced aspect ratio.
regarding the use of vortex generators:
they certainly work. however i believe the design operating condition is when angle of attack (AOA) is already high or near stall conditions.
i can see the benefit for commercial airplanes attempting to avoid premature stalling before landing/takeoff or the need for a fighter jet to operate at extreme AOA.
Even the bumps on the leading edge of whale fins have been shown to generate vorticity which maintains lift at high AOA.
however all of these conditions are typically quite far removed the the low AOA an 'efficient' wing would operate at to maintain optimum lift/drag ratio.
i dont believe any of the above vortex generators have proven benefits a low AOA where separation or stall is not likely.
perhaps as peter sugested, you may find benefits at extreme operating conditions of your foils where its more important to generate lift desipte any drag peanlity
regards,
-bill