I'm looking at the details of .SHARED files myself so I can share with you some of my understanding.
First thing to note is I really don't think you can take a .SHARED file form a QlikView version 9 installation and copy it to a version 11. It simply isn't going to work. I would recommend that if you for some reason have a need to copy SHARED files between two different QlikVliew installations that you make sure they are using IDENTICAL versions. you never know what changes Qlik may be making to the internal structure of the .SHARED file between versions.
.SHARED file do not contain application data. That's is data that is loaded into a QVW using LOAD statements. .SHARED files only contain information regarding the definition and layout of reporting objects.
I don't think Qlik document anywhere the structure of the .SHARED file. I'm guessing It's binary and it's compressed. Using the power tools QVSharedFileViewer you can export the contents of the .SHARED file to XML and as you have found that xml file can be surprisingly large. If you take a look at the contents of that XML you will get a view as to why it is so large.
If a user creates something as simple as a list box QlikView needs to store quite a lot of information in order to specify EVERY attribute of that list box. So you can imagine the definition of a complex chart can result in a very large block of XML. Look for a tag in your XML that starts something like
and follow through that entire GraphProperties tag and you will begin to understand why the XML file is so large.
It is my guess that the .SHARED file does not contain this actual XML. It has it's own efficient storage mechanism and the QVSharedFileViewer translates the .SHARED file structure to an XML representation for easier human reading.
Regarding your user1 user2 question.
If user1 creates and object and user2 needs to see it, user1 will first have to share that object either with all user or specifically with user2.
user2 will then be able to view that shared object in his repository and will be able to drag that object onto a sheet to view it.
All user objects are store on the .SHARED file but they are not actually shared until the owner decides to share the object.