The benefits from this talent will increase your regeneration while casting and while not casting by the same amount. That amount will be the first two numbers of your intellect stat (10%), making the benefits from this talent very easy to calculate.
Dreamstate's potency changes with your intellect stat; therefore, you will gain more of a benefit from this talent with raid buffs and it will scale with your gear.
Tips and tactics
If you spec into Dreamstate, do not start to gem and enchant for pure intellect, as the benefit from doing this is not as great as geming and enchanting for spirit or MP5, even if you also have Lunar Guidance.