You can also expand vocabulary orally too. I don't think it is as effective as reading aloud - based on my sample of three but it certainly helps. At primary level I had/have one fantastic reader, one good reader (eventually) and one who struggled. Even the one who struggled is praised for their wide vocabulary and often knows words more advanced readers in the class haven't known.
From a fairly young age we have included them in adult conversation and I deliberately use a rich vocabulary myself with them. So when walking past an empty, boarded-up shop. They asked 'why is that shop like that?' I would tell them that it was derelict rather than just saying it was empty, abandoned etc. That sounds like performance parenting but it would just be done in a normal conversational manner. I would explain a meaning if asked or leave them to infer if they seemed happy. It was quite deliberate and conscious, particularly at first.
It isn't quite as effective because they don't see the word and so spelling is more tricky. It is also partly down to the individual child. The one who excels in reading even before reading fluently was collecting adult idioms and phrases. He talked late just before two but read early. Around the age of three he would say phrases such as 'phew, we got there in the nick of time'. He delights in acquiring new words and will always seek to adopt a more complex phrase when a simple one would do. When out for a meal he would say 'I am toying between having x or y' rather than 'I'm not sure whether to have x or y.' He would always ask if he was reading or listening and didn't know what a word meant, whereas the others might be more inclined to let it pass but if questioned wouldn't be able to define it. I think some of those behaviours are just his natural disposition not his upbringing.
Other strategies you might adopt include flash cards, using a thesaurus, having a word of the day. I am not sure that these are as effective as reading and hearing complex words in everyday speech but you could certainly adopt a different word to discuss over breakfast each day wouldn't work in our house as you couldn't hear it above the chivvying, but your house may be more organised .
I agree too with all the advice about reading classics, you don't need to go too far back to get to a different cohort of language. I would say maybe thirty to forty years. You do need to read aloud together though to pick up on the language which some fluent readers find frustrating. With one of ours we used sticky notes which she would put in her book when she didn't understand a word. Not quite as effective but she wasn't as keen to read aloud when she was older.