So in some guides quoted on the interweb about shaman healing you'll find it said that 1 mp5 is equal in value to something like 5 +healing. I ran some calculations the other day that I will repeat here which are the basis of why I consider 1 mp5 actually closer to 2-3 +healing in value.
The calculations are based on this thought:
"How much +healing do I need to cast a spell at a lower level while still getting the same healing done as the higher level spell. And vice versa, how much mp5 do I need to cast a higher level spell while still spending the same amount of mana as if I were casting a lower level spell."
Let's get to it.
In my example of how to do the calculations I'll be using Chain Heal R1 and R2 as a resto specced shaman:
R1: 247 mana - 379 healing
R2: 299 mana - 479 healing
52 mana difference.
100 healing difference.
Chain Heal is a 2.5 second cast which means it gets 2.5 / 3.5 = 0.714 of +healing applied to it.
100 / 0.714 = 140 +healing required for R1 to become equal to R2.
So we've established that you'll need +140 healing to basically use R1 instead of R2. By using R1 instead of R2 we are saving 52 mana per cast, or 104 mana per five seconds. So for this example we do 140 / 104 = 1.34, meaning 1mp5 = 1.34 +heal.
Then we can basically do the same thing for all the different ranks. I'll save you the time since I made a spreadsheet for this already:
CH R1-2: 1.34
CH R2-3: 1.39
HW R5-6: 1.77
HW R6-7: 1.96
HW R7-8: 1.99
HW R8-9: 2.09
HW R9-10: 3.05
LHW R1-2: 1.82
LHW R2-3: 1.92
LHW R3-4: 2.05
LHW R4-5: 2.10
LHW R5-6: 2.29
Notice that Healing Wave R10 is a serious outlier, but obviously it will rarely be used. Regardless the average mp5 value is equal to 1.98 +healing but as you can see it's more valuable when using Healing Wave or Lesser Healing Wave (especially the higher ranks). Also keep in mind that mp5 has value while dropping totems and running around. Despite few fights involving a lot of those things (how many times do you spend 10+% of the fight not casting?) I think it's fair to say that on average 1mp5 is worth 2-3 healing.
Let me know if you want me to clarify something.