13 years is a lot of experience to speak of roger. I can't say I know what would normally go into a media arts personal statement but if it's like other general personal statements, speak of your 13 years of professional experience (ie. spotlight specific achievements), talk about your knowledge of the industry so that you're letting the admissions officers (or whoever's doing the selections) know that you know what you're getting yourself into without any misconceptions of the industry or your future. Let them know what you want to get out of the course and what you want to achieve post-graduation with the MA.
And some important qualities they will probably want to see is maturity, focus, and genuine commitment.