While I have some very fond memeories of vanilla(even beta) I wouldn't play on a vanilla locked server. Well, maybe for a little bit, but I wouldn't stay long enough to make it worth them opening one.
I loved 40 man raids, they were fun and challenging and really felt like an accomplishment. The newer styles (10 and 25) don't seem to provide me with the same sense of fulfillment that the 40 man raids did when we down bosses. It's still fun and enjoyable but something about 40 people going into an instance and coordinating everything was truely epic in the sense of a "raid".
That being said.... I hated grinding mobs for items to sell to have enough gold to buy a 100% speed LAND mount (it took me a long time to grind the money out for the 1,000G when i was lucky to get an item that was like a 15s vendor price). I enjoy being able to fly everywhere now. I remember getting my Dungeon set and enjoyed it, but as it has already been brought up you ran the same one or two instances at a point hoping to get that last piece (and i had it all.. forl ike 2 weeks until i started upgrading with MC pieces, then with BWD pieces until i had all the BWD stuff, then was about to staart upgrading naxx pieces, but only got one piece and didn't want to lose my set bonus from my BWD piece)
That and the talent trees and everything are so different now and I like it the way they are now. My druid can legitimatly tank, dps, or heal where in vanilla you healed and that was that, paladins were cleanse bots and that was that, shamans were healers and that was that, warriors were tanks and you tanked or you didn't do anything, priests were healers and shadow was laughed at other than for leveling purposes, etc. etc.
Anyways, just some of the reasons as to why I wouldn't play a server locked to vanilla content.
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"...and they'll say "Hey, Look at him!, I'll never live that way". And that's ok they couldn't anyway..."