Someone who uses one essay for a college class, as the basis for another, longer essay, for an entirely other class?
Yes, as long as you are just ripping yourself off, no problem. You should recast your old work for the new class.If you actually wrote the first draft and aren't ripping off some poor unsuspecting sod, then sure, why not? As you said, you're expanding and elaborating on a former idea or concept, as opposed to handing in a regurgitated "copy" of exactly the same thing, then what could it hurt? If the topic is applicable to both classes,....more power to you.
It's a bit like a rebounded double stroke for mine.....two hits for the price of one.