the basic angle of incidence for the wing is fixed by the attach fittings at the wing root. washing the wing "out" at the tip flattens the incidence at the tip, which decreases angle of attack and lift. it is the approved way to rig so that when the wing root area stalls, the outer wing still flies and lateral stability is still there. and, the ailerons still have some control. so ya, I suppose if you get rid of wash it would give a slight bit of increase in lift compared to what it would have if rigged per instructions. what happens then when you stall though is it all goes away at once with no warning... no lift, no stability, no aileron control. ya sure, maybe you can practice & be OK but when when it bites you is when you don't expect it... maybe a bit over gross, a bit steeper turn, a bit of wind shear, hot day, high altitude, whatever.... it will be the day you discover what an accelerated stall really is
other things guys did to boost low speed performance and get quicker take offs was to rig the flaps and ailerons slightly drooped from the fared position. that would get you off quick, improve slow flight, but costs in drag at cruise.
dihedral.... remember the 4 forces. lift is always vertical and opposite gravity. for a given wing size, more dihedral means fewer square feet of wing lifting. when the plane rolls though, the wing that moves down will produce more effective lift. the one that moves up produces less. that provides positive roll stability which means the aircraft will right itself after a disturbance.
there is pitch stability too.... down force on the tail, cg ahead of the center of lift, etc and in order for an aircraft to be certified it has to display this three axis stability. the rigging is a critical part of that design. the manufacturer defines the rigging procedure and alternate riggings are illegal and potentially fatal. and, there is no alternate wing rigging for a cub on floats