Genre roll call...
My first writing attempt was fantasy romance. Since I was only eight, it truly lacked on the savvy romance part. It was seven illustrated pages long. My more ambitious second try, at thirteen, was a fantasy rip off of Krull. It was about a hundred and ten pages. At eighteen I wrote another fantasy, this one more complex and actually novel length. Then came a fantasy novella, then a vampire novel set in modern times, then a 152k word epic sword and sorcery fantasy, followed by a demon in modern times novella, an urban fantasy romance with angels and demons, an urban fantasy romance with completely made up creatures, and then the published Persephone Alcmedi series which is urban fantasy with a little romance and a little smut. I'm currently working on a collaboration that is part urban fantasy, part action thriller.
You don't need a crystal ball to see my trend towards fantasy, be it urban or utter this-isn't-earth fiction. But none are repetitively the same, either.
I don't have the ammo to make a case for broad multi-genre writing. It just ain't me. But that doesn't mean I'd poo poo anyone's decision to branch out far and wide. As KAK said, genre is a construct meant to group books based on reader's expectations. It's a good thing, as I'm not often shopping for biographical vegetarian cookbooks. Seriously, the last thing I want is some bookstore getting healthy advice on a meatless lifestyle mixed in with my dystopian sci-fi.
"Wait a minute..." **lightbulb in my head flickers** "A whole new genre all my own." **lightbulb flashes and goes out** "Nevermind."
As always, the bottom line is write your story. Be brave. Try new things--that may be characters, setting, theme, POV, or genre.
I think the important thing is that YOU PUSH YOURSELF as an author. Push to learn and grow. Push to find the best carriage for your story. Your stranger in a strange land idea isn't working as a Victorian romance? Try it as an earthling-as-the-alien. Try it as runaway-princess-in-*insert the name of your made up world here*. Just never give up on yourself or your story. Keep writing. Sometimes that means unlocking self-imposed doors and stepping outside the comfort zone of your preferred genre. Even if its just a small step, it'll be one in the right direction because you'll be having a new experience. I guarantee it'll spark some creativity!