I think "stiffing" by removing or lowering the automatic tips is DISGRACEFUL. If you paid thousands for your cruise, you can afford $10 a day extra for all they do. Just because there's one bad apple doesn't mean they should all suffer.
As someone mentioned, you may want to give that special steward or waiter a phone card or some other tangible gift of appreciation that they can keep and use themselves. You could bring along some of the Costco phone cards, as they are good for all over the world. Probably the BEST non tangible gift would be to fill out one of those "above and beyond" cards that they have everywhere at the end of the cruise. Be sure to get the crew members full name and department. It will go in their permanent record that they have gone above and beyond the call of duty.
Also remember, the $10 only covers the waiters, assistant waiters and room stewards. If you get exceptional service from other crew members, tip envelopes are certainly appropriate there. For instance, as a parent and former teacher I know the Youth Staff in the Fun Zone do a wonderful job of keeping the kids happy and OUT OF SIGHT, all at no extra charge. I bet those girls could use the tips!