I purchased an extended warranty on an identical car as you in Nov.
2009 335i Sedan, MT, Sport, Premium, Nav
Gold package 7/100 (extended from 5/2013 to 5/2016)
I reality is if you aren't going to work on your car yourself, then you should purchase the warranty. Read the forum, the typical repair is around $1200. Think about the repairs you have had thus far...on a "newer" vehicle no less. Repairs generally don't decrease when you rack on the miles.
On a side note, a considerable amount of the turbo failures are not related to the extended warranty you are talking about.