Skip the next two paragraphs if you're short of time, they just give reasons :-).
Try to get into the mind of peple like the colleagues in my network. You are busy with your daily duties as a working and teaching scientist or engineer.You are not overly interested in programming. A year ago or so you discovered that SageCell enables you to do useful things that you couldn't do before and you invested the time to find and learn the 10 SageMath commands that you need to solve a few specific problems. and built your worksheets from these (well, maybe not even that, perhaps you just got your worksheets from a friendly colleague.) and you use them regularly.You're happy with these and you don't have a reason to invest any further time into tooling up - your sheets work reliably over a year.
One morning you come to your desk or to your class and - bang - find your code broken; frustration. You are under time pressure, your Sage knowledge is limited and rusty. Suppose you find the python-3-user page, you'll not find it too helpful (you had never been working with Python and you have just a vague idea what an iterator might be, you are reluctant to set up another account to report your problem - you just want the damn' code to work again as it used to and as effortlessly as possible)..
Summary: SageCell is so mature that it is used by people who have no deep interest in it.
Short answers:
No: The Python-3-user-page is not useful for all SageCell users.
Yes: This page is useful as an augmenting information why certain solutions work.
Yes: I volunteer to set up something simple for collecting problems, solution recipes and links to augmenting information but I cannot fill those in.