Well, on the subject of 1984... it was written in the mid-1940s, as I recall, and published in 1948 (hence the choice of numbers, only transposed); and Orwell was drawing on what he saw happening in Russia for his model of the society in the novel. I'm not really sure quite how much Wells influenced people as far as advancing space travel... that one may well remain an open question; most of the advances in that field came from much later causes, and even as late as the early 1950s, the majority of the populace were complete scoffers at the idea. And in the U.S., we were so sluggish with it that it took the fear of the Soviets beating us to it to get us moving.
Sputnik 1 - Wikipedia, the free encyclopedia
Up until then, we'd been rather slow in moving on this. Still, Wells certainly caused a lot of young people to dream in new ways, and perhaps some of those were the ones who began the early rocket experiments. Verne is more likely the one for that, though, as he did spend more time with the mechanics of it than Wells, who saw his as "scientific romances".
In general: can they affect the future by their writings? Yes, certainly. As can any writer, artist, filmmaker, etc. (Remember the influence of Wagner and Nietzsche on the Nazi party, for instance.) But such influence is, with rare exceptions, unintentional and, as I said earlier, in everything I've seen (with the possible exception of someone like Goodkind, who seems determined to preach) the sf and fantasy writers have stated repeatedly that they don't like the idea of prediction, but prefer to speculate and extrapolate according to the needs of the story and, if they are trying to make social commentary, it is in the nature of cautionary tales about where they see society headed, rather than trying to direct it in a particular direction (save away from the trend they are addressing).
