Line bottom and sides of a 6-quart slow cooker with aluminum foil; lightly coat foil with cooking spray. Stir together granulated sugar, brown sugar, and cinnamon in a small bowl. Toss together biscuit pieces and 1/2 cup melted butter in a large bowl until biscuits are coated.

Working in batches, add biscuits to granulated sugar mixture, and toss to coat; transfer biscuits to prepared slow cooker. Sprinkle any remaining sugar mixture over biscuits in slow cooker.

Whisk together eggs, salt, 2/3 cup of the half-and-half, and 1 teaspoon of the vanilla in a bowl until well combined; pour over biscuits in slow cooker. Sprinkle with pecans.

Beat cream cheese and 2 tablespoons softened butter with an electric mixer on medium speed until thoroughly combined, about 30 seconds. Add 1 cup of the powdered sugar and remaining 1 teaspoon vanilla; beat until smooth, about 1 minute.

Gradually add remaining 1 1/4 cups powdered sugar to cream cheese mixture alternately with 2 tablespoons of the half-and-half, beating on high speed until frosting is smooth, creamy, and a little loose, about 1 minute, adding remaining 1 tablespoon half-and-half, 1 teaspoon at a time, if needed to reach desired consistency.

Drizzle half of the frosting over biscuit mixture in slow cooker. (Cover remaining frosting, and set aside until ready to serve.) Cover slow cooker; cook on LOW until center of casserole is set and biscuit bottoms are browned, 3 1/2 to 4 hours. Drizzle casserole with remaining frosting; serve warm.