Boosing is still great, as you move fast, so the xp per hour is still good as you could run the same instance 2-3 times in 1 hour with the lower char on autofollow.
Good thing about this too, is you have access to ALL the loot. Meaning your lower char, will have blues in pretty much every slot. This can help massively when doing quests on your own.
Also, you can help finish the elite quests in each zone, at your own pace.
This is what I did when boosting my other chars on another account.