Being in a heavy traffic,in a heavy rainy day,this little devil drawn on my windshield by raindrops told me that in Random House of the English Language "showcase" is 1.a glass case for the display and protection of articles in shops,museums,etc; 2.the setting,place,or vehicle displaying something in a trial basis;vt.3.to exhibit or display., in Webster's Dictionary "showcase" is 1.a glass close case for the displaying and protection of articles in shops,museums,etc; 2.an exhibit or display usually of an ideal or representative model of something; 3. the setting, place or vehicle for displayng something on a trial basis; vt.3. to exhibit or display. ,in Longman Dictionary of Contemporary English "showcase" is a glass box containing objects for people to look at in a shop or an event or situation that is designed to show the good qualities of a person,organisation,product,etc.
So "street showcase" is no more than the name says.Your discussion was about a part of street showcase which is called "street photography".These discussions are not new and I am sure they will continue.
Thank You for these extensive comments