I have often run into the problem of sitting down to "write a nice little story" of maybe 4,000 words, gotten about halfway, & counted it out at like 6,000. The "5K barrier" is something that looms over me & I tend to respect more in the breach.
Every once in a great while, sure, you can get a complete (or mostly) short story that has enough legs to morph into a novel. I'm reading Killer in the Rain, a collection of eight Raymond Chandler stories that were all heavily pilfered to create his novels. While he was alive, he refused to allow them to be reprinted because he'd already "cannibalized" them & didn't feel it'd be fair to his audience.
But being very familiar with his novels, I didn't feel in the least abused. In fact, he hadn't simply swiped them whole by any stretch, & each story has its own unique moments that didn't make it to novelization.
dyljos, you're running the risk of "productive-seeming screwing-around" rather than writing & finishing stuff. If you get an idea that'll make it a good short story, then make it a good short story & get it out there. You can always go back & plagiarise yourself later.