"only 4% more SP" well.., considering that usually you have 2-3 casters in a 10man group (usually no problem w. buffs in 25man) as well as 2-3 healers that puts it to 4-6 players benefitting from the 4% gain as compared to Arcane Intellect, which quickly adds up, seeing as people in decent gear sits around 10k spell power they will gain 400 extra spell power, in a 6 min+ fight that 400 spell power isn't minor any longer.