Combine first 4 ingredients in a large bowl; beat at low speed of an electric mixer until coffee granules dissolve. Stir in brandy and Kahlúa; chill 1 to 2 hours. Pour into a punch bowl.
Combine whipping cream, powdered sugar, and vanilla; beat at high speed until stiff peaks form. Dollop whipped cream onto punch; sprinkle lightly with additional cinnamon.