I have no idea if it is a common knowledge or not and no idea if it was intended or it is a bug but Blessing of Wisdom stacks with Greater Blessing of Wisdom. Personally I did not know about that until yesterday when in raid we were buffing up and 2 pallys buffed me with blessings. First with greater second with normal.
If it matters:
1. First I recived GBoW from 1st pally.
2. Than BoW from 2nd pally.
didn't try it with same guy. Below screen shots with me unbuffed:
and me with 2 blessings:
the difference between mana reg is: 402 - 320 = 82 => blessings stack.