I can see why Glyph of Lifetap is better than Glyph of Incinerate for raids, the buffs you get will increase you spirit by a fair ammount, so that makes sense.

But as I don't raid much, usually just pug heroics at the moment, I don't always have the buffs to increase spirit. I worked out that I wouldn't even gain 100 SP after lifetapping... so in my case, would Glyph of Incinerate work out better?