1. Prepare grill to medium-high heat.
2. Combine lime juice, olive oil, cumin, garlic, syrup, and hot sauce in a small bowl, stirring with a whisk. Place the shrimp in a shallow bowl. Drizzle 1 tablespoon of the lime juice mixture over shrimp, tossing gently to coat. Reserve the remaining lime juice mixture; set aside. Thread shrimp onto metal skewers. Lightly coat corn with cooking spray. Place shrimp kebabs and corn on a grill rack coated with cooking spray. Grill 8 minutes, turning kebabs once and turning corn frequently until browned. Remove from grill; cool slightly.
3. Remove shrimp from skewers, and place in a large bowl. Cut kernels from ears of corn. Add corn, chopped lettuce, green onions, cilantro, black beans, and plum tomatoes to shrimp. Drizzle reserved lime juice mixture over the shrimp mixture, and toss gently to combine.
4. Divide tortilla chips evenly among 6 shallow bowls; top each serving with 1 cup shrimp mixture. Combine sour cream and diced avocado in a small bowl; mash with a fork until well blended. Top each serving with about 1 tablespoon sour cream mixture. Serve with a lime wedge, if desired.