I actually like Niagara in the winter, when the ground can be covered in snow and the falls get icy. Whether it's worth the long drive, up to you. But if you do go there, I'd do BOS-Niagara-DC-NYC-BOS, shorter that way, and less tome on the often-congested I-95. And as others have said, train for the DC-NYC-BOS portion is an idea worth considering.