For those of you directed here from Wowhead, this is an old post based off of pre-cataclysm numbers. For Cataclysm spirit/int relationship calculations please head to one of these two pages:
I was pondering some numbers from the Elitist Jerks board and it did get me thinking about the value of Spirit as it stands right now at level 85 in cataclysm. While mana should always be an issue when we raid, we still need an economical way to approach our regen.
I can’t take credit for the notion behind this example as it came from GreenTouch over at the EJ forums:
Currently one Rejuvenation costs us 3725 mana. If you divide that by 12 you find out how much mp/5 is required to recoup that cost over one full minute. In this case it is 310.4 mana or 310 mp/5. In order to achieve 310 mp/5 you would need roughly 620 spirit. Even with the increased amount of stats on our gear that still would take you 2 or 3 pieces of gear just to achieve a 1 Rejuvenation per minute regeneration rate. This is using: 1pt spirit = 0.5 mp/5
Let us comparatively look at our regeneration tied to intellect to calculate an equivalent weight. I am not aware of a new conversion so I might mistakenly use 1 int = 15 mana and talents being multiplicative for the purposes of my math. If someone spots a mistake or incorrect assumption I will gladly revamp my math.
To check the mana gained per point of int (using Furor, HotW, MotW, Leather Mastery): 1*(1.06)*(1.05)*(1.05)*(15*1.15)= 20.16 mana. For int based regen per minute I am using the following statistics: 8 ppm Revitalize, 1/3 Innervate return, and 100% uptime on Replenishment. This yields: 6.66% innervate + 24% revitalize + 6% replenishment for a total of 36.66%. That 1 point of intellect will provide 20.16 mana as well as 7.4 mana per minute. This would put each point of int at .62 mp/5 not including the benefit of the initial mana gain and inherent spellpower gain.
Including the max mana increase from that 1 point of int your math changes a bit depending on the length of combat:
1 minute: 2.30 mp/5
2 minutes: 1.46 mp/5
3 minutes: 1.18 mp/5
6 minutes: .90 mp/5
With one point of spirit at approximately 0.5 mp/5 and one point of int yielding 0.90 mp/5 it is hard to opt for spirit in any situation where we could also have int. The balance I can only assume is that they wanted to be able to add more regen to healer gear without the risk of inflating spellpower for either caster or healer and I respect that design choice. The difficulty would arise in gem,enchant, and reforging choices where a player might want to choose one over the other or opt to reduce spirit. With int offering a lot more by way of starting mana pool and spellpower it seems to win out in the end. For spirit to really shine as a healer stat it needs to be beefy so that with later tiers of gear we actually feel empowered with all of that spirit we have. If it continues to be weak (and I consider 620 spirit to regen one rejuv. weak) then you may see druids reforging a chunk of their spirit away for haste, crit, or mastery.
EDIT: Corrected math to include leather mastery per Hamlet’s comment as well as Revitalize ppm down to 8.