I don't think I could change my speech pattern or vocabulary, I've had it for too long. I didn't ever simplify it for my children, they learnt to say Thank you, never 'Ta', which I have often heard.
soon I think the more you read, the more you learn, without even realising that you are doing so. If you read books that are a little out of your usual comfort zone, you also pick up a wider vocabulary. You can usually get the gist of a word's meaning by the context in which it is used. If you don't read much, maybe you could try it.
Yes, I did notice that your speech pattern changed when you were passionate about a certain subject. Your speech became more fluent. Maybe you weren't overthinking it at the time.
So, are you saying also that regional dialects shouldn't exist? The people who live where they are still used don't always know that their speech is different. My daughter went to school with children who had never left their county of Lincolnshire - how would they ever know that the Cornish vocabulary can be so different? Or the Scottish? Nothing they hear on television would ever prepare them, because the news programmes are so localised.