ONE OF THE MANY gratifying aspects of Dike Blair’s ten-year sculpture and painting survey, “Now and Again,” recently on view at the Weatherspoon Art Musuem in Greensboro, North Carolina, was how it allowed the artist to fully exercise his understated but considerable talent for exhibition design. Though he operated well in advance of the design-as-art environment of the mid-1990s, transforming galleries into corporate lounges that worked as ambient takes on mass architecture, Blair left behind installation art per se many years ago. This exhibition’s subtle staging, however, managed to come just