I think that some of the quests you will encounter are really tutorials for end-game type material. I try to do all the quests I can, for in the end, I'll learn something new that will eventually pay off when I reach 70. Also, when you get to the end-game chains (68-70), you will already have built up the patience. Such as the Shadowmoon Valley chain, the gear you achieve is pretty decent for something that you will have been used to. Collection quests such as the termites in the Plaguelands and the Cones in Terokkar are very annoying to me, but sometimes Ill be in the mood to do them. Its almost as if you don't think about it. So my final advice is do whatever you're in the mood for; afterall, this is your leisure time ;P.