I don't know if I would call it real tough anymore after all the nerfs. You should glyph Renew (Or at the very least never glyph Flash Heal). You're not going to be begging for mana as long as you get two fiends/hymns off in the encounter and you're not going crazy over Searing Plasma, so don't fret about your gear or your spirit. It's fine.
Healing the encounter is pretty simple. Heal through the roll -> Handle Searing Plasma and tank damage using Serenity -> AoE heal through superheated -> DPS tendon. If you do that six times you win. Almost the same as normal, except if you're assigned to dispel Blood Corruption you'll have to do that also. You can glyph Dispel Magic for that. It should morph into the earth version after 2-4 dispels, and it will never morph back into Death. Get two stacks on your tanks, then after that try and get it on people who tend to get threat on bloods. You'll have a lot of bloods at the end, so you'll want to pay more attention to anyone that has threat on them.
I normally used GS on someone who had a lot of Searing Plasma left and was probably going to die from imminent damage (Happened quite a bit during progression). I used Hymn during a superheated usually. As for raid cooldowns, you won't need strong cooldowns for superheated as long as your raid is good at getting Amalgs as low as possible without killing them too soon. You'll want your strong cooldowns for rolls, and especially so considering that you don't have a Spirit Link Totem to use.
Lastly, make sure your raid is using Lightwell. This isn't a very hectic fight even for a DPS breaking grips, there's no reason not to.
1. I've heard on 10 man Spine people use Serenity but I'm not sure if this is true for HSpine. So I really dunno, since I run 25s.
2. I was told Spirit/Crit was best for Holy Priest on HSpine due to Crit being the only stat that affects Renew (aside from haste breakpoint) which will be your main heal here. Though, again, maybe 10-man is different somehow... idk
That's true on 10 heroic. I wouldn't gear for crit on 10 though, you're in Serenity so much.