See new thread for 2.0 Changes - Sorcerer / Sage Healing Compendium Updated for 1.2!)

[Kaedis]

You get more Bonus Healing from Power (0.1887/Power buffed, compared 0.1725/Willpower buffed). However, by the same logic as applies to DPS, Willpower is still superior in overall healing. For DPS Sorcs, Willpower is 10-15% better than Power, with Power providing 3.6% Bonus Damage. Power provides 9.4% more Bonus Healing than Willpower, so by that logic, Willpower should be 4-9% better for healers, for raw healing output.