Civic gurus shot down a developer’s proposal to build a four-story mixed-use building in Vinegar Hill, with locals fearing a rash of new, oversized building projects in the low-rise historic district.  “These new buildings could be more than twice as high as the historic brownstones and be forever totally out of character with the low-rise houses of Vinegar Hill Historic District, which we so much want to protect,â€� said Monique Denoncin, a longtime Vinegar Hill resident. “The unguided explosion of development that we experienced in Dumbo will then come our way. We do not want to be a reflection of Dumbo.â€� A lawyer representing the Spinard family, which owns a roughly 6,500 square…