Most important stat for priests

In my last raid I got the token for my T7 trousers, finally. That means that apart from one excellent jewelcrafting trinket, my complete gear is now epic (item level 200). Actually the trinket is item level 200 too, it just has a blue name. Anyway, while running around in full epic in Naxx-10 means I'm unlikely to get many further gear upgrades, I started to think more about whether I have the right gems and enchantments.

What I did was choose mostly gems and enchantments that add to my spirit. As a holy priest, spirit does add to my spellpower. But more importantly it adds to my mana regeneration. As I recently mentioned, I can't manage to run out of mana any more when soloing, and I last a very long time in a tough raid boss encounter. That is very much old school raid healing: During level 60 and 70 raids, a wipe occured when the healers ran out of mana. Thus mana regeneration was the most important stat, because the longer you could keep healing without running out of mana, the longer the whole raid survived.

But I'm wondering whether this is still current thinking for level 80 raid healers. Nowadays I very rarely see a fight last so long that I'm even getting close to running out of mana. Is spirit still the most important stat for holy priests? I could easily imagine to re-gem and enchant all my gear with +spellpower, which would raise my spellpower by about 200, but lower my mana regeneration per 5 seconds by over 300. So each of my spells would be more powerful, but I could cast less of them. Which in many cases in Naxx-10 wouldn't matter at all.

I'm a bit reluctant to switch, not because of the considerable cost (I have 3 prismatic gems alone, worth 200 gold each), but because I'm not quite sure whether I'd really be happier with spellpower. Because while I might not need all that mana regeneration, I'm not sure whether I really need more spellpower either. People very rarely die in our raids, and if they do it is because they weren't healed fast enough, not because the healing spells were too weak. Plus in patch 3.1 the way mana regeneration works supposedly is nerfed, so I might be changing right back again.

So I'd love to hear from other healing priests: What are the most important stats for you? Do you go for spirit, spellpower, intellect, something else? How high do you think spellpower and mp5 should be (buffed) for a healer?