With the exception of primary healers, most notably holy priests and restoration druids, most players tend to consider Spirit to be the most useless Attribute, since it is only good for restoring Health and Mana.
... the small increase in Health regeneration is nowhere near as great as restoration through food or bandages.
Now why is this any different for mana? The regen from drinks is a level of magnitude more important than spirit regen.
I find that when I'm in boomkin mode that I'm out of mana much too quickly for mana regen to be worth much, even md5 regen. Wrath is a very cheap spell at 255, but when your battles last less than 30 seconds, typically, you'd need 8 mana regen per second to make any difference worth mentioning. So I'm usually maxing out damage rather than mana regen when I'm picking out boomkin gear
Innvervate is useful, as it allows full spirit regen during battle, and I can use it to keep a steady stream of wrath & moonfire coming down. That's about the only place spirit seems to be horribly useful for me. Even Elune's Touch seems to be more helpful than mana regen without innervate.
What am I missing?
I'll post later, but for this week, I've mostly been running Isle dailies. This has given me the opportunity to get really used to fighting the same mobs. I notice that it's easier to boomkin the warlocks, but it's more sustainable to panzer the meleers.
Sustainable, as always, means how much time I have to take recovering between mobs. With panzer, I can quickly bandage and continue, and with the right timing, using innervate and treants to keep the party rolling. With boom, I'm typically going down for drinks and food (with a shadowmeld) between each mob. So boom's not sustainable; panzer, at least with melee mobs, is.