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I don't think you have anything to worry about.

Firstly, as you said yourself, is your work worth stealing? And I don't mean your work in particular but all of our works. We're amateur writers, and if we consistently put out great work, then we'd probably be the first to share it with the world, way before any content thieves dropped by our portfolio.

Secondly, you're copyright protected. If you find one of your stories published almost word for word some place, then you can go to the publisher with data from WdC showing that you uploaded the story before the other author submitted it, marking you as the creator. Publishers don't take plagiarism lightly and they do talk to one another, so that author would probably have a tough time getting anything published for at least a while. And if that other author had made a good deal of money stealing your work, then you could always drag them to court. However...

Your ideas aren't copyrighted. Several people tried suing J.K. Rowling after Harry Potter because they thought she'd stolen their stories. Things is, she'd have to have taking their stories and either just copied them or rephrased them for that to be worth the lawsuits. Harry Potter contains a lot of ideas and story concepts that combined makes it into a great and unique story, but on their own there's really nothing special about them.

Boy a wizardry school? That has been done a million times before Harry Potter. Dark lord with a grudge against the protagonist? That's practically a cliché. Unwilling shape-shifting good guys? Done before. Every single idea has been done before (If you watch South Park, they have a great episode called Simpsons already did it highlighting this). It's your take on the idea that makes it original, and it's your take on several ideas combined that makes your story what it is.

So, yes, another writer could potentially read your stories and be inspired by your ideas. But as long they don't just copy or rephrase your work but use those ideas to create their own original work, then it won't be the same story. And them publishing their work won't make it less possible for you to sell your work.