Let them gather rested...when 3.0 comes out, the 60-70 xp required will be cut by almost half. If you consider double xp for rested + half xp required, you could spend 1/4th of the time leveling them if you wait a bit. Then again, if you have nothing else to do in the meantime, go for it! Try rotating the groups so one always has some rested xp.