I think you're making a mistake here; you're assuming that somebody does read the SAT essays in order to mark them. There's ample evidence (promulgated by Les Perelman, especially) that this isn't the case. Start with the realisation that markers are recommended to spend 2-3 minutes on each essay in total! Here are a few links that come to hand:
http://www.insidehighered.com/news/2007/03/26/writinghttp://www.nytimes.com/2005/05/04/education/04education.htmlhttp://www.nytimes.com/2012/04/23/education/robo-readers-used-to-grade-test-essays.htmlHonestly I would advise anyone to completely ignore anyone's SAT essay score; it isn't evidence of anything interesting.
I know someone who grades them for extra income, so there are are at least some actual humans involved.
The SAT essay is read by real people, but there are certain things they look for when they grade the essay. Use all the space given, use big words, and stay on topic with good examples.
A good example does not have to be a factual one, but one that supports your thesis. Take a read through this article on the SAT Essay:
http://www.applerouth.com/blog/2009/06/01/in-praise-of-folly-writing-the-sat-essay/
I just interviewed a young person who got a perfect score on the SAT, obviously including the writing part. I got the sense that you can work hard and learn how to write that kind of essay.
I looked it up on Google. Yes, there are many more perfect SAT and ACT scores now. Part of it is likely the plethora of study materials available, plus you can mix and match your SAT score parts to achieve a perfect score.
In 2011, there were roughly 360 perfect SAT and 700 perfect ACT scores.