Regarding spirit formula's for priests, mages, druids, etc. Are you sure that is right?
I could have sworn the old formula was 13 + spirit / 4 for priests, and 13 + spirit / 5 for everybody else. At some point that was changed to 13 + spirit / 4 for druids, to make them the second spirit based healer.
Also regarding mages, with the changes in 2.3, I don't know how many mages plan on keeping their spirit gear to swap around, because without that they make a rather poor innervate target.
It's also worth mentioning that currently, many priests use
[Earring of Soulful Meditation] (assuming your guild has progressed so far and it has dropped of course), which makes them prime innervate targets if they use it at the same time.