A guildie has just made that question and it made me thinking about it...
Right now I have like 11k reg combat and I'm doing pretty well. Divine Plea usage on CD, mana trinket on CD too, and in almost every boss I finish with 50-60% mana, and I'm only 503ilvl.
That's why I wonder if reforging some spirit to haste/mastery would be fine.
Have you tried it? What do you think about it?