Well, Trek is more sci-fi than Lost in Space or the Star Wars movies. Making the stories more realistic in terms of the science and technology would have made the stories pretty dull.
To make Trek more sci-fi, you would have to get rid of the transporter, all of the "humanoid" aliens (including Spock, of course), and add in the stretching/slowing of time from travelling faster than light, assuming that FTL travel would even be possible.
It's a myth that the level of scientific accuracy defines how "sci-fi" something is. Science fiction is fiction based on conjectural scientific or technological advances and their consequences. There is no requirement that the advances be genuinely possible, merely that they be treated as hypothetical science rather than magic or divine intervention, and that their consequences on human life be explored. A lot of science fiction begins with premises that are most likely impossible, such as psi powers or time travel, but explores their consequences in a realistic manner -- i.e.
if this impossible thing did exist, what effects would it have in the context of otherwise real science, psychology, and sociology? E.g. Alfred Bester's
The Stars My Destination: if humans gained the impossible ability to teleport anywhere at will, how would that realistically transform privacy rights, law enforcement, the transportation industry, etc.? The key isn't what the initial hypothesis is, but how convincingly its ramifications are thought out.
Scientifically plausible SF is merely one particular subgenre, known as "hard" SF. It's the type I personally prefer to write and read, but it isn't more valid or real SF than the "softer" kind, just a different flavor of SF. And it's got nothing to do with how intelligent an SF story is. There's a ton of intelligence in the soft SF of writers like Bradbury, Sturgeon, Butler, LeGuin, etc. The intelligence of science fiction is not just about its grasp of physics and engineering, but about its grasp of human nature, psychology, philosophy, ethics, and the like, not to mention the skill of its prose and characterization. Science fiction is still fiction, still literature, and its intelligence should be measured the same way you'd measure the intelligence of a mystery or romance or political thriller or any other genre of story. If it's well-written, if the characters are well-drawn and their actions and choices believable, if the plot is not cliched or obvious, if it makes the reader or viewer think, then it's intelligent. A crime thriller or courtroom drama can be intelligent in its portrayal of its characters and the ideas it expresses without needing to go into detail about forensics or legal technicalities. A hospital drama can be intelligent without needing to focus in depth on anatomy and surgical procedure. Such stories certainly
can go into that kind of detail for added texture and as a stylistic choice, but that choice isn't what defines the intelligence of the story, because ultimately stories are about people and emotions and ideas, and that's where the true intelligence of a story lies. And the exact same thing is true of science fiction.