There are second order benefits, like slowing down with less acceleration, so your coffee won't spill, but compared to the infrastructure investment and privacy issues, those things are really negligible.
Without the extra information, it's a completely reasonable decision to start overtaking. And then you slow down as well, after spotting the same information. So yes - V2V would help here.
Only reasonable if 'defensive driving' is a curse word in your dictionary. Otherwise it makes sense to wait a bit and see if you can detect something too. BTW, Google reported radar working 'through' at least one car, it can look through the gap between the car and the road surface. And LiDAR can see through glass of a car in front, or just over its top (the sensor bump of the car in front down' cover much of you car's view when cars are separated by several car lengths).
