You might want to take a look at Riverside Publishing's CogAT "Short Guide for Teachers" if you haven't already:
http://www.riverpub.com/products/cogAt/pdf/cogATshort.pdfAs far as why 113 would constitute a GT id score for NV, I have no idea. I've never heard that before. Each of the subtests and the total test have a mean of 100 and a std deviation of 15, I believe. 113 falls below the 80th percentile, or just on the border btwn high "avg" and low "above avg." It is nowhere near the "very high," stanine 9 area that is usually included in GT identification.
Of course, I've seen kids score totally differently on the CogAT vs. the WISC or another IQ test (my younger dd included), so I wouldn't automatically assume that a child with a NV score like that is not visually-spatially gifted. However, a score of 113 on the CogAT NV alone doesn't indicate that he is either.
If you are looking for resources for enrichment for kids who are strong in VS, you might want to take a look at Linda Silverman's Visual Spatial resource page here:
http://www.visualspatial.org/She has a whole list of recommended resources/enrichment activities:
http://www.visualspatial.org/links.htm