> most of the time I do find some interesting nuggets of wisdom, though I never make notes on them
Copy and paste them to a text file. (Think of not doing that as throwing your life away.)
Arrange them by topic later, as the file size gets unwieldy. Read and reread them, which hopefully will be hard not to do, as they are your favourite quotes. Write little comments and commentaries on them as you wish – illustrative examples from your life, things it reminds you of, parts you don't quite agree with and why, etc.
I've also started writing my thoughts to the notes file, e.g. all ideas I have for something to do. Without doing this they'd just be idle thoughts soon lost. I've started making LaTeX PDF books out of stuff from the text file, one for the current year and others for particular topics as they become big enough and branch off. I just wish I'd started 30 years earlier! To the notes file goes anything of any significance that passed through my head and might be of value later. Sorting that into topics, and whether it's my or someone else's words, comes later.
I've come across many mentions of writers (from the last few hundred years) always carrying a notebook, and writing thoughts, ideas, images down in a notebook. Other people then read their books and think they're deep thinkers. Maybe, or they just realized the value of their thoughts — priceless — and never let one go to waste. e.g. Emerson's notebooks, Lichtenberg's "waste books" (more concentrated nuggets of thought, from a scientist/thinker). Emerson couldn't write the way he wrote – his essays are stuff from his notebooks of many years stuck together.
This Book is my Savings Bank. I grow richer because I have somewhere to deposit my earnings; and fractions are worth more to me because corresponding fractions are waiting here that shall be made integers by their addition. – Emerson, journals, Nov-Dec 1833
When a book and a head collide and a hollow sound is heard, must it always have come from the book? – Lichtenberg
There are very many people who read simply to prevent themselves from thinking. – Lichtenberg
The three practical rules, then, which I have to offer, are, – 1. Never read any book that is not a year old. 2. Never read any but famed books. 3. Never read any but what you like… – Emerson, (VII 196)
You must keep two objectives constantly in mind when you are reading if you are to read wisely and judiciously: firstly to retain the matter you are reading and to unite it with your own system of thought, then above all to appropriate for your own the way in which other people have viewed the matter. That is why everyone should be warned against reading books written by bunglers, especially when they include their reasonings and arguments: you can learn of various matters from their compilations but – what is to a philosopher just as important, if not more important – you cannot learn from them how to bestow upon your mode of thinking an appropriate form. – Lichtenberg