Great summer salad! I even think you could make this without the shrimp, since my favorite parts were the sweet grapes, toasty walnuts, and peppery arugula. You can't really distinguish the grapes in the dressing, but it is light and refreshing, and a lovely pastel green shade.
I substituted a combination of chopped Romaine and spring mix and added a bit of sliced red onion, but even without these small changes this still would have been an outstanding salad. Flavors and textures were excellent. Even hubby raved! This is our "new" New Years Day lunch meal.