You can actually simplify it even more if you like, by using a File System Task, instead of a Script Task to move your processed files once done. That way you don't even need to write any code!
Having just spent the past several days developing imports for multiple csv and xls files, I would recommend that a script task would be best to do the move. The move file task seems to be buggy, at least with variables, and the suggested work around of using a copy followed by a delete affects file properties such as creation date.