Gareth, in general, I would say that I agree. However, the situation with "core" is that somewhere along the way, maybe with 2.4 or so, the "core" ability to collapse sections was removed! It was fortunate for me to find your CT, which not only gave me back the ability to "hide" sections, but of course, improved upon it. So I really think that some kind of "core" system should be included in Moodle to allow the user to compress sections.
If Martin believes that add-ins are the way to go, then maybe a programmer can be assigned to maintaining those add-ins that are "Moodle Certified" so that that users know that certain features will be available in the future.
Everything that I am saying is just a suggestion. I am very pleased with Moodle and your own dedication to these great add-ins.