Sadly, this means that we will continue to repeat the same mistakes "for the first time". Knuth's literate programming, Alan Kay's Meta insights, Chandy and Misra's parallel work, and other fundamental quality gains will have to wait for another generation, assuming that generation ever gets its chance.
What I see are languages without standards "evolving". That is, they are making all old inventions but badly (e.g. Python has "closures" but only 1 liners. What a joke.) They "abstract away" complexity but badly (e.g. Ruby has gems but you have no idea what the ruby stack is really doing.). This is much different from Alan Kay's abstraction. To quote Stroustrop "C++11 is a whole new language!" And MapReduce as an "invention". Oh, please. The list goes on.
The worst part is the stupid hiring games meme. Solve our puzzle! Take our quiz! Show us your blog! How many angels can dance on the head of a pin? Make sliding colored blocks on web pages!
Experience is a valuable asset in most professions but is looked down upon in programming. Unless, of course, your experience is "exact"... "oh, we need an Oracle 10.3 database guru with stored procedure experience".
If you want to know what companies to avoid... look for the ones that emphasize "culture'.
Either something's wrong with me, or something's wrong with this profession.
You would lose that bet I'm afraid! To be fair, I've only ever hired one person over 40 and that was purely down to the fact that 95% of applicants I've received to any of my jobs to date are under 35.
You are right on one point, this advice is mainly geared towards younger professionals purely because someone with your breadth of experience I would expect to have plenty of worthwhile experience to surpass any 'popular' github repo.
As someone who is a programmer for 41 years, leads multiple open source projects, posts to github on a daily basis, and writes code every day I find this trend disturbing. I have interviewed for a job where I helped implement the compiler they use and I'm "not qualified for the job".
People ask me why I'm not in management. I've turned down several "promotions" in companies because I live to program. Why would I move from the top of my skill set to the bottom of a career I know nothing about?
So your advice is interesting but seems to have a target audience of recent graduates, not seasoned professionals. Look over your hiring record. I'm willing to bet that you have not hired anyone over 40, regardless of their github status.