What exactly would count as a wholly new and fully realised character for you, then ?
I'm not the best person in the world at telling what makes a character sympathetic to people who aren't me, but it seems that a certain degree of being able to follow a character's thoughts and feelings, understand them, or imagine thinking and feeling the same in the same circumstances is usually part of that, and if you're going to provide a character with recognisable bits of the human condition, to some extent they pretty much have to be familiar bits of the human condition.
There are some story shapes that do crop up again and again, and reading TVTropes, or any of those various arguments that claim there are only three/six/twenty/four fundamental stories and everything is one of those, it can be a bit of a downer. To my mind, most claims that there are only n fundamental stories, which are A, B and C... tend to use such broad definitions of A, B and C as to be pretty much useless, if not downright meaningless, for considering one's own story. I mean, "stuff happens" covers pretty much every imaginable story but not in a helpful way.
It doesn't make me particularly afraid to write about my characters and stories, because to my mind, genre SF is a mature field with depth and complexity and context and that's a thing to be used in my favour. If somebody reading my current work in progress, for example, had never seen an episode of Star Trek, it should work as a fun story in and of itself; if someone reading it has seen a fair bit of Star Trek they might notice the places in it where I have thought "this particular bit of world-building here is a corner of the universe that Star Trek glosses over or handles in ways I do not find particularly satisfactory so I have done this with it instead and if it succeeds it will work better." That kind of level of influence seems legitimate to me, though very much a thing of which i want to be conscious.
