In college I recall writing a script for a grade but with the concept from a documentary I saw. You see, ideas can sometimes come to you in many ways. Some go out of there way by going to a far off place to focus, meditate, and write. Sometimes my ideas as weird as it may sound, come from dreams I have in the middle of the night. I get up, and start writing. Other times I get ideas by simply watching other movies like this documentary of a real life story. Well, the thought came to me, why not make a script of it, change it up a bit, call it something else, and wholah, you have yourself a script. That's just what I did in that class. I did get a good grade from my professor and he was well pleased by it. Maybe one day I'll go back to it if I can find it deep in the college days archives and polish it up, and maybe actually do something with it.
Anyway, my point here is if you have old scripts from days back, keep them. As you progress to new stories, it's always a good to go back to old stories you've written that will give you a fresh viewpoint to polish it up. You will have new experiences, knowledge, and new tools to help you revise an old story. You never know, there maybe a production waiting to make your old story come to life!