Storage Industry Statistics

According to Wikipedia: The self storage industry is primarily a United States-based industry: of the 58,000 storage facilities worldwide in 2009, 46,000 were located in the United States.

According to the Self Storage Association: There are now approximately 49,940 “primary” self storage facilities in the United States as of year end 2011; another 4,000 are “secondary” facilities (“primary” means that self storage is the “primary” source of business revenue – US Census Bureau)

I would like to see somebody do a study to determine the overall value of things being stored in storage units and see what the trend line is.

Are people in the USA storing more expensive stuff, less expensive stuff, or about the same?