Just a little clarification -- RCI has 6,500+ resorts worldwide. I'm not sure exactly how many of those DVC has access to, but I believe it's in the upper 500's, but less than 600. Both numbers are probably moving targets, because the timeshare industry itself is pretty fluid.
Also, access to those resorts are the only things DVC members get from RCI. You don't have a full RCI membership, so you don't have access to any of their benefits, some of which (like Extra Vacations or Last Calls) can be substantial.