Before my opinions on tipping--a little background.
We had a different situation on Carnival Cruise...it was our honeymoon and on night 3 of the cruise, they moved us to a family section to undo a mistake on another group whose seating had been split up. We were at a table for 2--supposedly in front of the windows-but the view was blocked by a support beam.
We were humiliated on the night they presented us a cake--as we had plans--but they drew out the festivities for the evening. We walked out as they were going to do their parade--had one foot out of the dining room. Our waiter spotted us leaving and strongly insisted that we return to our table for our surprise. The dining room was presenting the cakes all evening--why we had to wait until after the dessert conga line, I don't know. But in any case we didn't appreciate that. When the cake was finally brought--they wanted us to smooch--and we did not feel comfortable as children were eyeing us every where. We are not PDA kind of people (at least we weren't at the time

We said we didn't want to do that--and again, it was insisted upon. So we complied and had them immediately wrap the cake so that we could leave.
Sorry for all the back ground, but I wanted the info to explain why we tipped as we did. At the end of the week--we tipped this waiter just for the nights we were in the dining room as we felt poorly treated and that they crossed their boundaries in conduct with us. We did tip at the current recommended daily tip per passenger.
We also refused to tip the Matre D' b/c he rudely dealt with us in the table switch and was ultimately responsibile for how we felt during the trip when in the dining room. And trust me that he was infuriated at this--but then he said something very rude to me as I left the dining room and I felt justified at my action.
I feel that any staff on ship must earn there tip. The exception--are the bartenders where you pretty much don't have a choice in the matter. If you feel the wait staff did an outstanding job than tip accordingly. If you or your children miss a few nights in the dining room, it isn't the wait staff's fault. If they did an outstanding job the rest of the trip, then you can tip as if you were in the dining room the whole time. In our case--the wait staff was not to our liking, did nothing to make us feel special. Where they tried to make us feel special it was very forced and uncomfortable. So we tipped the bookrate for only the nights we ate at his table. Since our previous table was taken by other people, we didn't go back to tip that waiter. Our room steward on the trip was fabulous--especially when we flooded our ADA bathroom (we didn't request an ADA stateroom--and that is a whole other can of worms). Since the room steward, in our opinion, went above and beyond--he earned the rest of what we didn't tip in the dining room.
To each his own, I guess. IMHO--tip what you feel they have honestly earned--tip less if you think they did below avg, tip the going rate if you think they did avg, tip more if they did something extra to make you feel special.
We did end up complaining to the cruise line. They gave us $250 for dinner as well as a voucher for a discount on our next trip.