That is interesting since some people say that you didn't have enough quests to ding 60. Low drop rates on quest items had you farming mobs longer. Meaning you'd have to farm "less" when you ran out of quests compared to if the quest items drop rates were high.
Only real problem i had with vanilla was the mana regen. It could've been a tad bit quicker but I remember how you had to wait 5 sec before it began to regen in raids fondly, I liked that part! Would just have loved if, when you regen, you'd regen faster.
Mana is what made tanks, other than warriors, almost not viable due to running out of mana and being unable to hold aggro due to that.