The world is a visual place, and the same is true of your campaign world. Speaking as a game designer, art is one of the most important aspects of a game. Don’t believe me? Crack open a Monty Cook game or your PHB: high-quality art is everywhere, and it brings up immediate responses from viewers. Set pieces like Horror on the Orient Express and most of the popular Pathfinder games also come to mind. At the campaign level, if you have access to good art you can convey a better story. I can't even think of a character that I haven’t tried to draw at the gaming table.