Preheat the oven to 400°. Butter and lightly flour a 9-inch-diameter springform pan, tapping out any excess flour. Line the bottom of the pan with a parchment round, then butter the parchment.
Sift the flour, baking powder, baking soda, and salt together into a large bowl. Beat ¾ cup of the sugar, 6 tablespoons of the butter, and the olive oil in another large bowl on medium speed until smooth. Beat in the eggs, citrus zests, and vanilla to combine. Add ⅓ of the flour mixture followed by ⅓ of the wine, beating after each addition just until smooth. Repeat with the remaining flour mixture and wine. Do not overmix.
Transfer the batter to the prepared pan and smooth the top with a silicone or offset spatula. Distribute the grapes evenly over the surface, pressing them in slightly.
Bake for 20 minutes, then remove from the oven. Dot the top of the cake with the remaining 2 tablespoons of butter, sprinkle with the remaining 1 to 2 tablespoons of sugar (as desired), and continue baking until the top is golden brown and a tester/toothpick inserted into the center comes out clean, about 20 minutes longer.
Let cool in the pan on a wire rack for 20 minutes. To unmold, run a knife around the edge of the cake and release the ring. Serve warm or at room temperature