Powerleveling each toon seperatly instead of leveling normally together might be faster upto about level 45ish. But after that it won't be worth it anymore much, I think.

I've so far doen all quests in Hellfire Peninsula + Zangarmarsh + Terokkar and just started in Nagrand. I've had a few quests that were pretty annoying. Terrokar wolf furs, etc. But it's worth doing them for follow ups and such. I would strongly recommend doing the collection quests too in Outlands. Sure it's a bit repetative, but you grind through the other quests quickly anyhow. And the exp is still worth it in Outlands.

Leveling in Azeroth upto 60, I couldn't be bothered myself either though. But Outlands is different. xP