so much text to go through. I'll try my best
ACCENTS/VARIETIESI think I should start by saying that varieties and accents are not the same thing. Accents are just the phonological features; varieties include accents plus at least one other subsystem. For example, British English and Australian English are different varieties not only because they have different accents, but also because they have differing lexicon and semantics etc.
Therefore, the accent continuum does not depict sub-varieties of Australian English. It may be true that those who speak towards the Broad end of the continuum use more non-standard features, but it does not necessarily correlate. I remember stories being told to me about smart people being discounted because they spoke in a Broad accent. Take Julia Gillard for example - she speaks in a Broad accent, but definitely not in a Broad 'variety'.
STANDARDI'll preface this section by saying there is no standard. As native speakers, we all have different definitions on what is Standard. However, we generally concur on what is non-standard, therefore you never say standard features in your essays, but instead non-standard features.
Standard Australian English is the highest prestige form of our variety. Thus, rather than being spoken, it is written. We wouldn't generally write diminutives etc. unless it was casually. However, some Australia-specific lexicon is definitely part of SAE; words such as footpath etc. are used in prestige situations (at least, Wikipedia.) When it comes to Strine, it is not SAE. The best I can equate it to is the 'Broad variety'. In any case, the thing with Strine is that it mocks our Broad accent (I read some of the book. Quite hilarious.) which is not standard anyway. Think of ethnolects etc. as sub-varieties of Australian English (remember, as long as they have more than the accent going for them!).
With the whole lexical/syntax continuum, I personally think that isn't language according to user, but language according to use (phonology=accent anyway). I'm using more formal language here than I would speaking to my friends. Therefore, what I'm writing is closer to our idea of SAE because of its use. However, when talking to my friends, it's more informal, therefore I use more non-standard lexical and syntactic features. It may just be that our general idea of people who speak with Broad accents are normally in informal settings, therefore increasing the amount of non-standard features likely to appear.
The thing about thushan's classification systems (in the first post) is the subsystem they affect. Accents are purely phonological; varieties are phonological and frequently lexical, syntactic or semantic as well. I guess use the classification system that best suits your paragraph.
ESSAYSJust by thinking about it, some are meatier topics than others. I would personally think that all those topics that Plan-B mentioned could potentially pop up in a question together. You could have Standard English + Varieties + Attitudes or Varieties + Change + Attitudes. Codification would probably pop up with Standard English, I would have thought, however it's not really that interesting in my opinion.
ah, such a long post. feel free to ask any questions for qualification. I love doing uni lingustics
