The regrowth glyph is strong enough that it has the potential to create a heal style around it. First, the build is
27/0/41+3 aka Nature's Grace (NG) build. The +3 is because you have the option of Dreamstate or Living Seed, both of which seem to be reasonable options. You give up Flourish, GotEM, Replenish, and the direct heal/tranq talents. The big gain is Nature's Grace (.5s off next spell after crit, lasts 15s) but 9% cheaper Regrowth, 12% int->SP, and the ability to solo efficiently are nice perks.
So how good is Regrowth?
Assumptions
Coefficients from the tree thread-- My guess is that they'll have a fixed conversion for SP->Heal for all classes and keep the coefficients. Correct me if I'm wrong, I haven't done LK heal theorycrafting.
2500 +heal (whatever this works out to be in SP), deliberately low
No haste, which is slightly unrealistic because WoA should be present at minimum.
No overheal.
I'm
ignoring the HoT for this discussion and treat it as a direct heal spell.
Regrowth R12
Base Heal: (2494+2234)/2 = 2364
Bonus Heal: .289 * 1.2 (Emp. Rejuv) * 2500 = 867
Non-Crit Heal: (2364 + 867) * 1.14 (Gift of Nature + Master Shapeshifter) = 3683.4
Crit: 10% (base/int) + 50% (Imp. Regrowth) = 60%
Living Seed Crit Multiplier: 1.5+1.5*.3 = 1.95 best case, assuming no overheal on the crit
Crit Heal: 3683.4 * 1.5 = 5525.0
LS Crit Heal: 3683.4 * 1.95 = 7182.5
Expected Heal: 3683.4*.4+5525*.6 = 4788.4
LS Expected Heal: 3683.4*.4+7182.5*.6 = 5782.9
Cast Time: 1.5s * .6+ 2.0s * .4 = 1.7s
Mana: 1040 * .8 (ToL) * .91 (Moonglow) = 757.1 mana
HPS: 2816.7
HPM: 6.395
LS HPS: 3250.0
LS HPM: 7.378
Nourish (assuming full 71 points resto and imp ToL and Lunar Guidance offset each other)
Base Heal: (1883 + 2187) / 2 = 2035
Bonus Heal: (1.5/3.5) * 2500 = 1071.4
Non-Crit Heal: (2035+1071.4) * 1.14 * 1.2 (assuming hot on target) = 4249.6
Crit Heal: 4249.6 * 1.5 = 6374.3
LS Crit Heal: 4249.6 * 1.95 = 8286.6
Expected Heal: 4249.6 * .9 + 6374.3 * .1 = 4462.0
LS Expected Heal: 4249 * .9 + 8286.6 * .1 = 4653.3
Mana: 600 * .9 (Tranquil Spirit) * (1-.05*(4|3|2|1)) (GotEM) = 432 | 459 | 486 | 513
HPS: 2974.7
HPM: 10.33 | 9.72 | 9.18 | 8.70 | 8.26
LS HPS: 3102.2
LS HPM: 10.77 | 10.13 | 9.57 | 9.07 | 8.61
no HoT HPS: 2360.9
no HoT HPM: 6.56
So Nourish is a better direct heal when a target has a hot on it and a worse direct heal when it doesn't. Remember, this is comparing two different builds. A full resto will have a more expensive Regrowth.
So what about that glyphs?
Glyph of Swiftmend - Your Swiftmend ability no longer consumes a Rejuvenation or Regrowth effect from the target.
Glyph of Regrowth - Increases the amount of your initial Regrowth heal by 50% if your Regrowth effect is still active on the target.
Glyph of Rejuvenation- While your rejuvenation targets are below 50% health you will heal them for an additional 50% health.
Regrowth R12+Glyph of Regrowth
Non-Crit Heal: 5525.0
Crit Heal: 8287.5
LS Crit Heal: 10773.8
Expected Heal: 7182.6
LS Expected Heal: 8674.3
HPS: 4225
HPM: 9.49
LS HPS: 5102.6
LS HPM: 11.46
So, with a regrowth on the target and the glyph, Regrowth becomes a better direct heal than Nourish. In fact, the expected heal is close to HT R14, which is 8070 non crit.
My vote for the glyph to pair this with in a NG build is the Glyph of Rejuv. A Regrowth on someone < 50% has a 60% chance of catching a 1.5s
12.4k direct heal, which is a 3.7k seed. A full resto could, of course, put out the same heal, but the value of NG is that the heal has an extremely high chance of landing .5s sooner. It's like a mini Light's Grace. This is fast and (probably, given the TC healing numbers I've seen in other threads) strong enough that you should be able to heal reactively if you've got the buff, especially since you've got a seed and a full HoT stack on the tank. It's anti-spike without cooldowns.
Now whether this will actually work in a raid is questionable and likely to depend on your heal group makeup (you'll need someone to aoe heal at minimum from the look of things), but it looks like a great general purpose/5 man build. Bear in mind that all the numbers above are completely ignoring the HoT, which gets the lion's share of the SP, so the HPM numbers can potentially be much better. Finally, the really low coefficient on the direct portion of Regrowth means this won't scale that well, but it's fun to theorycraft regardless.