It's up to you. You can try to send it to magazines that have a higher acceptance rate (but, because of that, may not have as wide an audience and/or may offer little or no payment.) Or you can try to self-publish it. Or you can just chalk it up to writing practice and stick it in a folder of, "Awesome Stuff I Will Totally Sell Later When I'm Rich and Famous."
The problem is that if all you've got is form rejections, you don't know if it was rejected because of a writing issue, or the editor's taste, or whatever. You can have a guess, but as the author, your guess is going to be way biased.
If by "mine for parts," you mean take lines you particularly liked and try to force them into another story, that rarely works for me. Maybe I can re-use a character or setting, but single lines don't transfer well.