Collector’s Fallacy
I think app collecting falls under the Collector’s Fallacy umbrella. I do the same with books. I see a book that sounds interesting, order it, and put it on the shelf. Sometimes I read part of it. Rarely, I read the whole book. I do this to an extent with journal articles, and of course web links to Pocket.
As far as apps, many of the ones mentioned by OP, plus DEVONthink, The Brain, Tinderbox, etc. Although I’m putting Tinderbox to good use thanks to @beck’s excellent videos, as well as the new edition of The Tinderbox Way (which I’m actually reading).
Good discussions:
by Christian Tietze at his zettelkasten site.
by Charles Chu over at Medium
Both of which draw from Umberto Eco’s How to write a thesis
Edit 01/24/2020 Tinderbox has gone wonky again, and quick links don’t work as expected. Dev response is slow. I’ve been using roamresearch.com as of late. It has fewer bells and whistles than TB, which is sometimes an advantage.