Felicity, I agree. It is quite obvious that what really bugs Emma about visiting Miss Bates is the private visits she has to make. Ther's no evidence that at a party she is less than polite.
And in all honesty, I would say that most people would find a private call on Miss B tedious as well. Miss B is a nice woman and she's poor and deserves kindness and patronage. But that does not mean that she's interesting to talk to and naturally Emma finds it tiresome to have to listen to her yakking on and reading Jane's letters ten times over. It does not mean that its Ok for her to not visit more often, but I can perfectly well understand how boring it is to have to go and see her as she knows she ought to do and why she fails in her duty sometimes. AFAICS she does not fail in practical kindness such as sending them food and so on but she does fail in her social duty at times...