Consistency adds verisimilitude. No consistency, no verisimilitude, and the whole thing becomes an exercise in surreality. Some people bitch about George Lucas changing things between the OT and the SE, or the OT and the PT. Other people bitch about EU writers changing things from the movies. I liked the movies, so I don't like it when people ignore them and make things up.
Furthermore, the Star Wars universe is a setting that can support many genres of storytelling. Film purists sometimes pick up an EU book, see that it's not a good-vs.-evil epic with a smattering of Eastern philosophy, and give up on the whole thing. And that is their right. (Heck, I pretty much gave up on it when I saw they were going back to the epic style.) Some of us delight in writers that tell new stories, in new modes, using familiar elements. You want military specops? Comedy? High-level political and martial strategy? Romance? Fantastic alien cultures and life forms? Epic science fiction history? Highly detailed references to a created world? Metafictional stories about the power of Star Wars itself to inspire people? All of these and more exist in Star Wars.
One of the reasons Star Wars is so compelling is that the films continually hint at the larger universe. That adds verisimilitude. (There's that word again.) The EU has given talented writers, et alia, many thousands of pages to explore the rest of the universe and tell stories about it. There's nothing wrong with that. It gave us a fleshed-out Wes Janson. That alone makes the entire enterprise worthwhile.
I haven't read Shadows of the Empire in about a decade, but I don't remember any hard science in it. Not as much as, say, a Michael Crichton novel. Or even that Hardy Boys/Tom Swift crossover where they travel back in time in a truck. That was an awesome story, and I wish I still had my copy.