Speaking strictly from an engineering stand point, wheel spacers would be neutral to turning radius, but the downside to wheel spacers is the increase in bending moment applied to the spindle and bearings. Installing spacers may allow you to reduce length of wheel stops, thus permitting a tighter turning radius without tires interfering with body, frame or bumper, allowing you to reduce the turning radius. The downside is the tighter you turn the more you stress the axle u-joints. A lot of axle and drive shaft u-joints have been broken by getting them bound up under load in a tight turn and applying too much throttle. If you want to use wheel spacers to allow wider/taller tires go ahead, but I would not reduce my wheel stops.