My impressions are based on pulling a flat nose trailer (Trail Lite) vs our current V-nose (VR-1) with the same truck.
Are they significantly easier to tow? Overall, I would say no real difference. Straight head winds seem to be a little smoother with the VR-1, but quartering headwinds were worse than the flat nose.
Does it improve your mileage at all? Not in our case.
Does it...help with sway or wind from passing vehicles? No difference with vehicles overtaking. A little less buffeting from trucks in the opposite direction.
In my opinion, the real advantage of a V-nose is maximum floor space for a given length.