No, don't wash it before a show. There are so many criteria that judges use, and a lot is subjective based on the preference of any particular judge. Mainly they look at overall impact in color and design, then piecing accuracy (perfect points, seams lined up across sashings, etc), quality of the stitches in the quilting (they will scrutinize the back), density of the quilting (enough, too little or too much in their opinion), quality of the binding (full of batting, precision of the miters in the corners, properly done joining point not just one end slipped inside the other). If you want to see a lot of bloggers and websites talk about it and get judging sheets from major shows, just google "quilt judging criteria".