http://forums.worldofwarcraft.com/thread.html;jsessionid=3DEFCBC4996CEEC694D73E53E4D449BB.app05_07?topicId=8202534426&sid=1I was confused (a little) by the new "Spell Power" statistic, so I went on various fan sites, message boards, and calculators, and found that there are generally 3 points of confusion about it, and here's the rundown:
1) Everyone will roll on the same thing! There'll be less gear for me!
First of all, you should rest easy with "omg everyone will roll on the same thing" as a problem. It won't be an issue due to this:
In the current system, let's say a boss drops both a spell damage piece and a healing piece. Also let's say either of these has a 25% drop chance. One can reasonably expect that on average, 1 in 4 runs will drop a spell damage piece, and 1 in 4 runs will drop a healing piece. So if a group has a mage and a priest, and no other casters, it will have to run 4 times each to get it (on average).
Now with the "spell power" statistic rolling both spell damage and +healing into one, there will be just one piece of "spell power" gear, that has a 50% drop chance. On average, the same group as above will also have to run 4 times to get it (on average).
The good thing about the new system is that you won't have to deal with the random "2 +healing pieces dropped in a row - we'll just have to vendor/disenchant it" problem. So the new system will work in player's favor, in terms of actually getting gear.
The problem that I see is: this will greatly reduce the uniqueness in the look of casters. In a 5-man group with a mage, a warlock, and a priest, the tank can look behind him and see 3 nearly identically geared people... hardly aesthetically appeasing.
2) Healers are getting gimped!
On first look, one might say, "hey, now that there are no more +healing gear, won't the healers get less healing power?" Well, the answer is no. Healing spells will ALL BE BUFFED to have a higher coefficient to use the new spell power. On average the healing spells be be roughly the same as a similarly spec'ed and geared pre-WotLK character.
3) Hybrid healers will be too powerful
Some would argue that since healing spells are automatically upped to roughly equal the current healing power, getting the new spell power will give healers too much spell damage.
While this may be true to a small extent, talents and damage spells are being adjusted to reduce that effect. Also, talent trees are 10 points deeper now, and there are many very deep talents that either increase healing or damage. And hybrid healers won't get the spell damage talents to match what pure spell damage classes are getting deep in their trees.
So at level 80, healers won't be too powerful damage-wise, in my opinion.
Hope this demystifies the Spell Power statistic for you!