Toss tomatoes, 1/4 teaspoon salt, and sugar in medium bowl; let stand for 30 minutes. Transfer tomatoes to salad spinner and spin until seeds and excess liquid have been removed, 45 to 60 seconds. Return tomatoes to bowl and set aside.
Strain tomato liquid through fine-mesh strainer into liquid measuring cup. Bring 1/2 cup tomato liquid (discard any extra), shallot(or green onions), vinegar, mustard, and honey to simmer in small saucepan over medium heat. Simmer until reduced to 3 tablespoons, 8 to 10 minutes. Remove pan from heat and cool mixture to room temperature, about 5 minutes. Whisk in oil and black pepper to taste until combined. Taste and season with up to 1/8 teaspoon table salt.
Add pecans,blue cheese, and dressing to bowl with tomatoes; gently toss and serve.