You must live in an interesting area to find things like this in a thrift store.
Bellingham is a college town, there are 4 colleges here including a state university. Out of about 92,000 people almost 30,000 of them are students.
They come and they go, when they go some of them donate.
There is a large retirement community as well. People pass on and their progeny come to town to work out what to do with their belongings. Some of that ends up at thrift stores too.
I'm not a hoarder, although I am an accumulator. I try to flip things as often as possible and I do donate myself.
All that said, I used to find amazing things in Fresno when I lived there. Larger population but maybe not as dynamic or vibrant in culture. I really think the key is to look often and only buy stuff that you know you could get your money back out and then some. Or something useful, like gig bags. I got a nice padded Roadrunner electric guitar bag and a padded Ibanez bass bag yesterday for $7.50 with tax.
Recently I picked up a pair of DCM Corp TimeFrame TF400 hi-fi speakers for $10 at Goodwill. I had to solder a speaker cable to one of the lugs since the threads were broken off but they work perfectly and sound really, really good. I bought a 100 year old flamed koa ukulele there for $5. It needed a few minor repairs but I sold it as-is for $500. In Fresno at Starvation Army I found a Gurian guitar that needed repairs for $70, got almost $1,300 for it.
It's a hobby but I like hobbies where I either make some money or save a lot. One time I found an Audio Technica microphone in the tools, It had tape goo on it but it cleaned up nice and sounds good. Condenser mic made for live vocals - $3. One of my best mic stands started life as a Gibraltar cymbal stand, I added a dual mic bar instead of a cymbal and it's great for mic-ing acoustic guitar - $12.
I could go on. Get out there and look around, people have stuff!