Is the factory supplied nav systems on gm cars worth the 2 grand? Wouldn't the onstar turn by turn be as good if not better. I wonder about road changes or closure updates that a preloaded system wouldn't have. Does anyone that has experience with both systems have input? Are updates provided on the navigation by the factory? I'm not interested in the add-on market gps. thanks for any advice. Are there any drawbacks you care to share?