because this same staff also works in the buffet and MDR lunch, so it's not like OP is not going to use their services at all.
so, do you have unlimited specialty dining, and will never use the buffet for breakfast or lunch, MDR for breakfast or lunch, Solarium bistro if applicable, or any other eateries besides the specialty ones? At all?
I still wouldn't cancel auto gratuities, though. MDR personnel are not the only recipients.