I think all we agree that Amplify is surelly worth on fights against non caster bosses ( Sartura or Patch for example ).
But what about caster Bosses ( Emperors for example ) ? The tooltip say: Damage taken from spells up to 75 and
healing spells by up to 150. On Emperors for example we use the only tanks strategy and 6 healers on each of them.
With an improved Amplify my LHW does heal +100 more per wave, considering the rate of our healing is higher than
emperor bolts ( if any ) I do think even on a fight like Emperors one Amplify Magic is the way to go.

Do I miss something somewhere ?

I've been trying to work on my guild about using this more often, but they're generally pretty apprehensive sadly. It seems to me that on nearly ALL fights the extra healing will be worth it.

The one exception I think would be stacking dots. I got a poison from the crypt fiends at Anub, and it ticked for 306, while one of the tanks said their single stacks would tick for 250... that would start to add up quickly.

We've started using it basically everywhere on the MT and frequently on significant OTs too and I'm quite happy with the result. As for Patchwerk, you'd have to be mad or foolish not to have a mage spec magic attunement for that encounter. Having a priest-Atiesh in every healer group would provide less of a bonus than the talent adds to the standard spell. And the standard spell is twice that amount of course.

I think we use it pretty much everywhere now, Exception is probably the likes of Vael where magic damage taken is a constant. Adding +30 per tic on HoTs, and with low rank healing spells (R4 HT, Heal Rank 2) it's a nice boost.

While not end-game, Amp magic on everyone at General Rajaxx in AQ20 is amazing.
The extra healing from the buff means you need alot less healing.

I'm sorry, this doesn't make any sense. Paladins don't get more from +healing, they get less than their counterparts. Rank 4 HT, Rank 2 Heal, and Rank 5 Healing Wave are all 3 second cast time (2.5 with talents) thus recieving 86% of +healing. Paladins equivalent Holy Light 4 is a 2.5 cast time with no way to decrease it, so they get only 71% from +healing.

He never said they get more +healing from it. They just benefit greatly from the +healing.

Boevis i prefer to think of it as healing wave would be getting 120% of the bonus. Since everything is relative to the 3.5 second time frame.

Paladins benefit involves downranking heals and spamming flash of light throughout an entire fight. From there you can decide to save mana for bursts or uprank a bit.

For a druid to get the equivelant benefit would involve cycling targets with rank 4 rejuvenation. You cast rejuvenation on 8 targets getting 225 extra healing on each one. Which is:

8 * 225 / 12 = 150 healing per second

The equivelant of +350 healing for a paladin btw but spread through 8 targets.

That works out (without looking up all druid specs) to roughly 933 HPS at 70 MPS for a raiding druid.

By comparison a paladin would be doing about 600 HPS at same MPS and gearing level.

Typically though on fights with a large amount of aoe damage the damage is magical negating the benefit.

(Gheal2 spamming priests would also get a significant benefit, the important thing is what proportion of your time you spend casting)

I crit our amplified MT for 2.7k with a rank 2 heal earlier in the week. That was... yeah.

The benefits in many cases outweigh the costs. We don't have constant raid-wise crazy use of the buff because to my knowledge we still only have a single mage specced for Magic Attunement, but we'll use it on tanks and such for a number of bosses.

Shadowflame isn't affected by amp magic?

How much damage would it add to a shadow flame exactly? 75 tops? Can Shadowflame even crit? I would say big spike spell damage fights are probably the best place to use it. Its like a drop in the bucket for damage, but makes healing back up quicker/more effecient.