I think that eyes in the back of the head would actually be a disadvantage. Any sensory gain would be all but negated by the practical necessity of keeping those posterior oculars concealed, in order to avoid falling under the crippling stigma society at large levies upon freaks. Not only that, any survival benefit in a danger situation - assuming one saw it coming far enough away to whip the cover off! - would be offset by the weakened structural integrity of the skull, what with those two extra holes punched in it right where it needs to be most solid.
Admittedly, the convenient situation of the occipital lobe and primary visual cortex, towards the back of the brain and right there ready for some hindsight-style visual input, might provide some unforeseen benefit. But it seems doubtful that any such benefit would be greater than negligible - certainly it would not be significant enough to overcome the negatives.