The point of an iLevel is to give a rough approximation (albeit mostly scientifically) of the value of gear. Gear that has an iLevel of 600 is better than gear that has an iLevel of 300. It's pretty easy math to do, and helps players in figuring out gearing progression.
But what it's not meant to do, I'm realizing more and more (and is what Ghostcrawler is getting at, I'd reckon), is be a game in-and-of-itself. The end goal of Mists should not be to have the highest item level possible. You can do that if you want, but at the end of the day those marginal improvements are not going to let you defeat the boss any better.
What does matter in defeating the final boss, much more than gear, is the skill and mistakes you have associated with a particular fight. If you can't run out of fire properly, then you're going to have a bad time. If you can't dance like you need to, then since Vanilla WoW, we've known you're going to have a bad time (and you won't be a friend of mine). Sure, gear might give you that extra 0.01% DPS boost, but you can't DPS when you're dead -- and chances are there are more things you can do with your class to increase your skill and provide more DPS than marginal upgrades in gear could provide.
So what's a raider to do? How can you, like me, change your gear obsessed mind to negate the marginal need for upgrades?
First, focus on the damage done, not the damage per second. Those with the highest skill, and arguably the better players, generally rank higher in total damage done. Back in Cataclysm I joined a new raiding guild and had absolutely terrible gear, but I always survived until the end of the fights. This earned me a spot in the raids -- my DPS was god awful, but the fact that I could outlast those well geared players and do more overall damage, that was my saving grace.
Second, focus on the end result. The boss is going to die, and when he does, then your gear has completed its purpose -- it has helped you down the boss. You really don't need more after that. Everything you get then is just ... well, in the true sense of the word, needless.
Third, understand your skill. While you can do a lot to make up for your skill with better gear, it's probably time to just have an honest conversation with yourself about how good at this game's highest levels you actually are. For 99.9999% of us (myself absolutely included) there are things we can do better with your class mechanics. I know I don't use my trinkets at the right time, and I know I don't time my DoTs correctly. That stuff? That's a helluva lot more important than any marginal gear upgrade.
In conclusion ... grab your towel and don't panic about gear.
Side Note: Yes, I'm sort of doing the press thing where I'm grabbing a sound bite and running with it, but I'm also giving a lot of context and depth here. So while we here at WoW Insider preach not to talk Ghostcrawler's quotes as divine motivations, given the context, I think it's okay for this one.