Here's a possibility for Mystery #13. It is the Simon's Coffee Shop once located at Wilshire and Fairfax: http://flickr.com/photos/79761301@N00/2092406462/
One more Simon's on Wilshire: http://jpg3.lapl.org/pics25/00062240.jpg
And another: http://jpg1.lapl.org/pics18/00008803.jpg
Some pieces of the streamlined facade of this drive in are reminiscent of the Coca Cola stand at DCA. Certainly, there's no Deco drive in like this one left standing in Southern California.
As for the possibility that Disney's Imagineers only borrowed architecture from extant buildings, I (slightly) disagree. Hollywood's Brown Derby was demolished in 1985 and this structure, http://www.flickr.com/photos/79761301@N00/2093063506/ , originally located on Wilshire in Beverly Hills, was demolished in 1988/89, years before it was added to the theme park in 1994, http://flickr.com/photos/79761301@N00/1087134986/ .