I think it has some value if you are a weak laner and worried about the opponent all-inning you within the first two levels, or are going for some sort of invade strategy where the shield will get broken instantly but still contribute heavily to your survival.
However, it is too far in the defense tree for it to be worthwhile on anyone but a tank or bruiser, and even then the later masteries should define your role, not your early game.
Moving it earlier in the defensive tree would make a lot more sense because the early masteries should determine how you play the early game, and Runic Blessing is distinctly an early game mastery. However, it may be too valuable if it is too early, so maybe require 8 points in the defensive mastery tree? That would be about right.