Trying to appease the hardcore audience can only end in disaster. Just look at what happened to Everquest.
Most guilds can't clear AQ40 reliably or even at all. Things like consumables or world buffs benefit those players the most. For the top end guilds having 15% more stamina or 10% extra crit means nothing, they can still clear the raid just fine without them, it just makes the fights longer, but for a more casual guild those buffs can be the difference between finally beating a boss they've been struggling with for months or disbanding the guild.
Same thing with buffing the boss' health or abilities. For people who whine about bosses being too easy, who have the mechanics down and can execute them properly, the boss having 50% more hp, or using an ability more often, won't wake any difference. They'll still be able to kill it, it will just take longer, and then next week they'll be back on the forums, again whining that it's still too easy. For everybody else however, even if you're able to kill the boss, the increased length means you'll need more consumables, which makes the fights even harder for those who can't spare the time to farm them.
In the end, the hardcore players will quit, because they'll think the bosses weren't buffed enough, the casual players will quit, because they'll think the bosses were buffed too much, and there'll be nobody left. You can't make everyone happy.
Besides, you don't change horses in the middle of a stream. It's best to just leave everything as is. It's what everybody expects and accepts. If they didn't, they would've never started playing at all. If they wanted custom changes to raids they would not have decided to play on a server that advertises itself as blizzlike.