I agree completely.

Although I am sure adding and maintaining quests that will be seen by only 1/10 classes is more difficult than most of us would estimate, I would still posit that this is one of the few elements of the game where the end result is more rewarding to players than the time it takes to put together would suggest. These things make the game seem deeper and more complex than it might otherwise seem- and that's a good thing.

I have similar feelings about the Ancient Petrified Leaf quest as Rossie does. My brother picked up the leaf and set about the quest. It was amazing to see the various things he was expected to do- and I know it changed the way he approached the class. It cementing kiting for him (which he would put to use in the Razorgore fight), it taught him the jump shot and actually ended up ingraining the benefits of key-binding.

I also have fond memories of helping my other brother complete his dreadsteed quest. The frantic ritual in Immol'Thar's room was unlike anything else in the game at the time. I barely understood what he was doing, but it was great to see him scamper to keep the thing going while we kept the mobs off of him.

If I think about the Warlock quest a bit, it really informs what I was saying before. I'm sure there could be a boss with similar mechanics to that ritual (heck, maybe there's even been one). However, quirky boss mechanics are never seen as anything more than that (heck, if they're difficult they can be seen as being far worse). However, when you tie them to something like a class quest, they are allowed to develop a mystique. Part of what make me look back on the ritual so fondly is the fact that we only did it a few times and the time we completed it we really had something to point to and say "Look- WE DID THAT."

I have fond memories of the warrior quests. My first WoW character ever, figuring out how to get the required items.

People were nicer back then. A friend of a friend (someone I never knew IRL) had a level 60 priest who was able to help me with that overpowered air elemental you had to kill.

Then there was the Sunken Temple quest. "Did everyone get the feather from that boss?" kind of thing.

My biggest issue with the whole "Only 1/10 people will see this" is simple. Legendaries.
Sorry, you make a legendary for ONE class and somehow this is okay. Make one for only DPS casters (5/10 classes there) and somehow that's fine.

Raids prior to LFR were things that, what, 5-10% of the players saw the end of? Why make those last bosses if only 5% of the players see them? Oh, because they want to see it. Some people wanted that end game content that was raiding.

Make something so that EVERY class will have a unique quest, oh, stop the presses.

The game IS poorer for it.

So long as they are soloable when they get past a certain point. Or so the rewards are not central to the class (mounts or abilities). I like them for lore. Not for practical purposes. Involving real dungeons now that we have the finders is cool too.