"I equally don't see any reason to believe either that they were properly frequent, or that Emma's rare self-doubt in their regard shouldn't include material comforts, especially when I read the complete text as I have quoted it above ".

I dont see why you think this. Emma is not neglectful of her duties to the poor who do need food and money type charity so why would she be mean or neglectful in this respect towards the Bateses? If she were, Im sure that Mr K would refer to this as it would be a far worse failure of duty than not visiting often..
And we're told that when the ladies were visiting Mr Woodhouse and he through his fussing about food, was trying to stop them eating hte nicethings, Emma quietly made sure that they were fed properly... so I can't see why you would think she'd forget or not bother to send them the sort of food and wine presents that were considered a "delicate way" of giving them soem extra food and helping them to eat well on their small income.