That spec could be tough. You would have to stack a ton of crit since you are missing the 5-8% from the ret tree since that is better mana regen w/ illumination. You could also stack a ton of mp5 like the good ol days and focus on that and int for Divine Plea.
I like the added benefits of the spec. I may have to acquire some more mp5 gear and give it a try.
6% extra heal and extra armor is nice, but most raids will have trees, and that effect is identical to those of the tree, so it becomes useless. (check stacking buffs posted by BLizzard months ago)
Guardian's favor is nice, but... 8% spell crit is better.
I can't say your spec is bad or good. And I can't say putting all points to ret is bad, because it really depends on your raid setup.
If you are a heavy raider, I will have 2 specs: 51/20/0, and 53/0/18
enlightened judgement is good for PvE. you can judge at range, saving you a lot of running, and also keep you out of the boss AE damage including cleave and other stuff. JoL is a must keep in 25 man. many people will gain the benefit from it.
I favor the first one. But that's cos I like damage and haste. haste is great because you can heal faster, dodging the spell lock. conc aura is overrated now, because we almost always heal with holy shock first. Then we get fast HoL if it crits, which it will.