30% less damage will play out like this:
Morchok: Will make a joke more of a joke
Yor'sahj: This fight feels pretty declawed since the nerf, another nerf will just further it.
Zon'ozz: 5% is maybe needed, 30% will be over kill, the black phase will become L-O-L worthy as it increases
Hagara: All the more reason to ignore all the mechanics
Ultraxion: After all these weeks of gear and you still can't kill it I feel sorry for you.
Gunship: On 10's it needs a slight nerf, on 25's the fight isn't that hard, honestly if you can't get 25 people to do the work of 10 just go sit down.
Spine: On Heroic, the initial nerf may do more harm then good. The fight is a balancing act where you have to kill a corruption and hideous elemental thingy at the same time. If you change the health of the corruption (and not the damage to break stun) you will have less time to dps the burning tendon, while it will have 5% less health that won't help the fact that the dps check will likely be impossible with 3 dps down.
Madness: It will make it feel even less epic.
My 2 copper
[Today 06:48 PM] Ion:swimming in a natural body of water ISN'T acceptable...it's momentarily tolerable