With 2 points in this talent, Amplify Magic (Rank 6) will increase damage taken by 180 and healing taken by 360. Dampen Magic (Rank 6) will reduce damage taken by 180 and healing taken by 360. Visually this talent doesn't affect [Dampen Magic/Amplify Magic] buff's tooltip with new correct numbers, ah boom, is it is a visual bug or an actual bug?
If you are talking about the tooltip on the buff (as in top right corner), it won't show the updated value. This is a Blizzard issue that was only changed in Cata. All improved buffs / debuffs only show the values of the base skill, not the updated values.