Finely chop 7 grapes; transfer to a small bowl. Cut remaining grapes in half; transfer to another small bowl and set aside. Using a fork, mash chopped grapes in bowl into a purée. Stir in shallot, 1 tablespoon Sherry vinegar, and 1/4 teaspoon salt and let sit for 5 minutes. Whisk in oil and 1 tablespoon saba. Season vinaigrette to taste with salt, pepper, and more Sherry vinegar, if desired. DO AHEAD: Vinaigrette and halved grapes can be prepared 8 hours ahead. Cover and chill vinaigrette and grapes separately. Bring vinaigrette to room temperature and rewhisk before continuing. Combine arugula and halved grapes in a large bowl; drizzle with vinaigrette and season with salt and pepper. Toss salad to coat. Arrange salad on chilled dinner plates, dividing evenly. Scatter cheese and almonds over. Drizzle salads with more saba.