You are mostly on the right track, although there is more history-of-the-genre context. There's a difference between terrestrial science fiction (predicting Earth tech and societal change) and travel sci-fi (speculating on external life, philosophy, far-futurism and large-scale physics). Technological acceleration feels primarily the former. Secondly, for imagining the impossible, that's what Douglas Adams always tried to do, intentionally writing his characters into a situation that is impossible to escape from, e.g. floating unprotected in open space, and then forcing himself to think of a highly improbable way of rescuing them, e.g. the infinite improbability drive which can put a ship at every point in space-time simultaneously, enabling the rescue. The trick is to write yourself into an impossible position, then expand your imagination and then invent something new.