I did all quests on my DK, but only did collection quests on my shamans when it opened up new chains without more collection quests. I'd say I did ~85-90% of all quests that my DK did on my Shamans.

Even if you factor in that collection quests took longer, it really wasn't that bad considering each one gave 16-22g plus an item that could be sold for another 6-12g on each shaman - even if the collection quest takes 20 minutes to do on all 5 chars thats still 125-150g in 20 minutes which isn't horrible. Plus this was balanced out by non collection quests that could be done in <1 min.