I generally prefer independent GUI files rather than "per test", so that if any aspect of the GUI changes you only need to change it once in the applicable GUI file rather than for each test's GUI file which references that GUI element.
"Any sufficiently advanced bug is indistinguishable from a feature." -Bruce Brown
As you refered in the query that the content is dynamic.
I guess the GUI Map file is the concerned if you add GUI Map objects Dynamically, because you will pick up the objects while executing the script and add the reference of the object in GUI Map File. So in this way there is no maintainable issue too, because you will not be saving the added GUI Map objects in the GUI Map file.
Don't take this the wrong way...but geez..who recommends that you use one GUI file per test for ease of maintenance? If it's someone you work with...send them to training! If you have a dynamic app - I can not think of a justifiable reason to do this unless you want to guarantee yourself a job for years to come fixing gui maps!