Stanford seems much more concerned with soft factors and is thus considered an admissions "black box." If you have killer rec letters and a solid personal statement, I don't think it's worth it
I'm spending it making a pros and cons list for Yale, Harvard, Stanford, Full-ride Columbia, Chicago, and NYU, fully knowing it will soon become a useless file.
I graduated 2011. If you have a professor you liked, it doesn't hurt to try to ask them. Refresh their memory who you are. Maybe dig up an old essay you wrote in their class and include.
... subpar writing. A DS and optional essays are there to provide ... writing skills. Mediocre to poor optional essays are worse than none ... you forgot a major (but optional) component and the quality is ...