With Enhancement's ridiculous mana generation, should you even care about Shamanistic Focus?
Personally I spam SS, Flameshock on slow-dying mobs, Earthshock, and Fire Nova, and still find it really difficult to run out of mana. And that's with switching between Water and Lightning shield (so some of the time water isn't even up)
I can definitely see that for certain types of pulls you should care about mana efficiency, and I don't spam Fire Nova all the time, but waiting for Shamanistic Focus seems odd (although you're really not usually "waiting" for it since it's up most of the time)