In a large mixing bowl, beat the softened cream cheese, sour cream, granulated sugar, and vanilla extract using an electric hand mixer on medium speed until the texture is completely smooth.
Add the washed and dried red and green grapes to the bowl. Use a rubber spatula to gently fold the grapes into the dressing until every grape is evenly coated.
Transfer the mixture into a serving bowl or a 9x13 inch glass dish.
Cover the dish tightly with plastic wrap and refrigerate for at least 2 hours (or up to overnight) to allow the dressing to set and flavors to meld.
In a small separate bowl, stir together the brown sugar and chopped pecans until well combined.
Just before serving, sprinkle the brown sugar and pecan topping evenly over the chilled grape mixture to maintain the crunch of the pecans.