The best way to make this decision is to weigh up the cost involved. If buying in the materials that you need to etch your file sharp is cheaper than buying a new file then you might want to consider giving it a go.
If you do choose to sharpen your file, it’s worth bearing in mind that it will not be as sharp as a brand new file.
Of course, if you’re an amateur blacksmith then you may have the facilities to re-cut your file yourself. If you don’t, though, the cost of re-cutting the file is likely to be a lot more than buying a new one.