I'm not sure what you mean by
"advanc[ing] the paranormal field." I think 'the paranormal field' is much advanced by the contribution of psychological insights to human ideations and compulsions of all types, including those termed 'paranormal'.
You seem to want to rule out such insights regarding Strieber by interpreting his persistent ideations as 'fiction' -- not only in his novels but also in his narratives of his own reported abduction experiences in nonfictional works. It seems that by defining him as a fiction writer you hope to define everything he has written as 'fiction', a category of expression which you seem here to define as
'imagination' severed from the common, shared, 'reality' that humans experience in the world. But works of fiction are necessarily connected to, grounded in, a world recognizable by other humans. If this were not the case, works of fiction (including cinematic works in the modern period) would not continue to draw us to read and watch them. It is, in fact,
narrative that draws humans to it, as it did in earlier narrative forms in human history -- legends and mythologies passed by word of mouth before they began to be written down.
Narrative interests us, in biographies, autobiographies, and historical works, as well as in novels and films, because it places us as individuals within a representation of the world we exist in. Works of science fiction and fantasy take us farther afield from the 'world' we are accustomed to, but they always retain core structures of the world as we interpret it in day to day life. Accordingly, narrative is a powerful tool in the hands of writers of many persuasions who hope to use their fictional works to change the perceptions of their audiences concerning the nature of the political, sociological, economic, interpersonal world we live in as a species, and also in the hands of writers who seek to take us forward into projected social futures or inward into examinations of our own consciousness.
Strieber seems to me, based on
@Liminalist's interpretation, to be a writer consumed by his own inner struggle to distinguish what is real from what is not real in his lifelong 'paranormal' experiences. I think he has written book after book as possible aids to discovering the meaning of what he has experienced. He is a confessional writer as well: he confesses his own confusion about his experiences, searching for ways to interpret what they signify -- and also their origin. This is why I think it is a mistake for anyone to take him as a guide to his or her own experiences, dreams, fantasies, fears, etc., no matter how similar they might seem to Strieber's. I think it's clear that he was 'messed with' and manipulated by a series of mind-control agents and functionaries, early on to make him immensely suggestible and deeply fearful, and later on to mold him and support him as the agent of a destructive mythology by which to control mass thinking about the ufo/eth phenomena. I doubt any publisher gave Strieber a $1-million advance to write one of his major alien abduction books. Who do you think was likely to fund that project? And why was it considered to be worth such an investment?