I recently decided to start doing old quests on my priest. I won't say that I'm trying for Loremaster, because I'm really not fretting about it... though if I did manage to persist that's what I'd be going for eventually. Maybe I'll just get to Seeker, or maybe I'll grow bored after two zones. I'm just experimenting with the general concept.
I really like quests, but the problem I always have nowadays is that I like instances even more, and ever since BC Blizzard has worked on making the latter much more appealing. Even back at level seventy when heroics were hard and not nearly as popular as they are now, they were still rewarding to run, with new badge of justice rewards getting added with every major patch and reputation gains actually being kind of a big deal.
But quests? I remember running quests past the level cap back in Vanilla, simply because there wasn't that much else to do for a newly dinged sixty. In BC I always cleared the first couple of zones very thoroughly whenever one of my characters made it to Outland, but never completed all the quests in Netherstorm and Shadowmoon Valley because as soon as I hit the level cap they just stopped being rewarding. I did a few more while playing with friends and to get decent starter equipment for dungeons and raids, but after that... eh. Now with the dungeon finder out, I struggle to make my alts above seventy complete more than one zone worth of quests in Northrend, and even my low level toons have discovered chain-instancing as a more worthwhile activity than questing.
It's kind of sad really. I love exploring the world and learning about all its little stories, but at the end of the day I also really like to advance my characters. And once a quest goes grey and/or you hit the level cap, quests just don't have anything to give you but a bunch of gold, which is pretty worthless in today's hyper-inflated economy. Dungeons on the other hand almost never stop rewarding me with better items (even if the rate of acquisition slows down considerably), plus I get to play with other people and be social. It's just no contest.
So, from that point of view, going back to do quests in the old world is a very odd thing to do. After all it would be much more rewarding to simply roll up a new alt and do it all at the right level, so I get to see new content and actually gain experience from questing at the same time. The only problem with that is that it's very hard to keep track of which quests you've done on which character. I reckon I've probably done quite a few out of the overall total, spread across all my characters, but with the current quest tracking system I can't very well know. Better to just get it all done on my priest once and for all, so I can say that I've been there and done that.
I do have to say, riding around Mulgore on my Amani war bear and killing level five mobs in my full Sanctified Crimson Acolyte outfit makes me feel like a bit of a tool though. You'd think that I'd enjoy showing off to the newbies or something, but in fact I just feel embarrassed. Whenever I spot a low-level character, I flush quietly and then give them a wide berth. I feel bad about destroying their private immersion of the quillboar being a genuine danger (because to a low-level character they are) by one-shotting them with my caster dagger. I feel like I'm shooting pigeons with a rocket launcher, while attending a sport festival in an evening dress - out of place in so many ways.
It is an interesting experience though. For example it makes you realise just how much of our questing time is actually taken up by running around. Contrary to what you'd believe, killing the mobs ten times faster doesn't make you complete the quest ten times faster, because you still have to run all around the zone to find just the right kind of kitty to extract a femur from, and then back again to hand it all in. That's not all bad though. It's nice to just move through the old world again and take it in in all its glory before the Cataclysm will change things forever.
And of course you do find little gems among the quests. So far I'm only working my way through the starter zones, which I already know pretty well - being an altoholic and all - but even there I haven't seen everything before. For example I was quite surprised to discover this quest a little northwest of Razor Hill, on top of a watch tower. And here I always envied the draenei and blood elves for their bag-rewarding starter quests... without knowing that the orcs and trolls had one too, providing them with nothing less than an eight-slotter!
It really doesn't seem to matter how long I play this game, there's always something left to discover that I simply didn't know yet. It's just harder nowadays to motivate yourself to actually go out and look for these things.