Actually ive done that before with a 70 druid running 4 druids thru instances right. Yea you get to lvl like 2 lvls per run but after a cpl runs u get so sick and tired of instances lol. You also have to be careful not to grab aggro with the alts so you need to leave your alts far back go round them up and aoe hehe. But dual-boxing is always fun and easy and you can lvl those 2 just as fast without having a booster due to you can still kill fast but you dont need to run around the world getting from instance to instance.