Yes, skip side quests, they are not needed anyways. I have 2 wizards in MB, my Myth guy has spent at least 15 hours doing every quest and still has the final 3 instances to finish. My Fire guy has logged about 6 hours so far in MB, skipping side quests, and only has Big Ben left to do.
In Mooshu, remember to do the Mossback side quests, it will make life easier later on (Obsidian Chest Quest, Life Rebirth spell quest, to name a few)
Is there an Obsidian Chest in one of Marleybone's side quest? ...probably