This smells heavenly! All fruit except bananas, kiwi and apples are a good choice for this fruit salad.
NOTE: If serving as one of several side dish items, most people will only take 1/2 cup and this should easily serve 35 - 40 people.
In a small saucepan, add the sugar and water. Zest the orange over the saucepan. Then split the orange and juice the orange to produce about 1/3 cup of orange juice. Add orange juice to the saucepan and stir to combine.
Bring to a boil, then turn heat to medium low and simmer for 20 minutes to thicken. While dressing is cooking, split vanilla bean and scrape out seeds. When dressing is done cooking remove from heat and stir in the vanilla seeds then store dressing in the refrigerator until cold.
Meanwhile, prep the fruit: Wash the berries and grapes and hull and slice the strawberries. Thoroughly drain the mandarin oranges.
When ready to serve, place fruit in a large bowl. Drizzle the dressing evenly over the fruit. If necessary, thin dressing by adding 1 - 2 tablespoons juice or water. Gently toss to coat all fruit.