Improved renew increases renews healing by about 8 per tick/talent point - so 24 per tick when you have all three talent points. That adds up to about 120 more healing per renew cast.
Looking at renews limited use in raids (most of it just becomes overhealing) I'd say that it's a somewhat questionable choice.
Spirit of Redemption is kind of like picking night elf for "improved death" - you don't want to die in the first place.
I guess it has it's uses in pvp and maybe vaelastrasz, but that's about the only places I can think of where it would be expected of anyone to die in current content.
So between Spirit of Redemption and Divine Spirit I'd take divine spirit.
I can't say I use prayer of healing often (I prefer to us Holy Nova on vael because it generates no threat, and leaves me more time to renew/flash heal other groups and mana isn't an issue during that fight anyway) so I can't speak at all about those talents.
This is a picture I posted 10 months ago here in the priest forum - when the server was still relatively new, I think most of it still holds true (maybe not the 10% mana part, but back then there wasn't a lot of +healing)

Technically the stamina and spirit talents are only required by 1 person/raid but that would lead to a lot of downtime, and on the other hand everyone in the raid could be running around with power infusion since healing isn't really a problem in current content - why not just let some mage kill mobs faster?