And there lies the problem.
This is a social forum with like interests and no matter how hard you try it is not going to change even if the mods take a hard line on topic diversion.
As you have noticed some threads go away from the topic to something completely or just onto social gossip.
I belong to a number of forums mainly technical ones and as soon as there is a crack down on going off topic people stop posting or post infrequently. Then when the pain eases people start posting again.
This forum has a great mix of technical stuff, basic help, advanced help and social chat. I like it just as it is, no matter how frustrating it can be tracking down the thread where you read something you want to revisit.
Mods do a great job keeping this balance.
Having said all that please start the process. Maybe even a new category rather than a topic in an existing category. "What happening in this photo" or "What is missing in this photo" or "Learning from Photos".
Photo's are worth a thousand words in explaining something simple but complex to explain in words. I like your thinking Cowgirl.