In a heavy-bottomed saucepan, bring wine, vinegar, shallots, and saffron to a simmer and reduce by about two-thirds, to ¾ cup. Add sugar. Slowly whisk in butter cubes, one at a time, incorporating each before adding the next and being careful not to let the sauce boil. Season lightly with salt and pepper to taste. The sauce should be nicely balanced with no strong vinegar taste.
Meanwhile, sprinkle scallops lightly on both sides with salt and pepper. Melt the remaining 2 tablespoons butter in a saute pan over medium-high heat. Sear scallops about 3 minutes on each side until nicely browned, but not overcooked. Spoon sauce onto warm plates, add scallops, and garnish with caviar (or minced red pepper).