I think if you go ahead and pay the automatic tipping at $10.00 per day, per person, you'll agree that the staff that is serving you all week truly works hard for those tips and deserve it.
If at any point you receive service above and beyond, then go ahead and tip a little extra.
When you order sodas or bar drinks, they will automatically add on a 15% tip to that. Its a totally seperate tip than the $10.00 you pay for your cabin attandant and wait staff in the dining room.
Hope that helps some?