I was given many pieces of electronics throughout my childhood 10-18 years old. In my earliest project, I made a 'speakerphone' through a Lloyds 3in1 stereo and had lots of fun. The Lloyd's wasn't really mercy gear, it was just family gear no one wanted so, I took it.
The first piece of real hifi 'mercy gear' that was given to me in college was an old receiver. I can't remember the brand... probably NAD or Marantz... One channel died almost immediately. The guy that gave it to me had hoped I would keep it forever and cherish it as he had. I threw it in the trash.... it was old and I knew nothing about electronics. Plus the guy that gave it to me was kind of a jerk other than this one kind act.
Fast-forward a few years....
I received a Hegeman Hapi 2 solid state preamp as 'mercy gear'. I bought a pair of B&W minipods.... and then sold my HK 6250 integrated amp to buy a B&K ST-140... After getting a new amp, I had officially begun a very cool journey into achieving the sound I wanted. The Hegeman/B&K/B&W combo was the best I'd ever heard and it wasn't expensive. I realized that everything doesn't have to be expensive.... just the speakers do.
Right now I have been in the process of selling every little piece of gear I don't need. Mostly cables... but, I have an old pair of Energy ESM2 speakers I don't know what to do with. They sound OK but, I'd love to tweak them.
Unfortunately, of all the stuff I've given away or sold very cheaply, I haven't really seen its effects. However, on the receiving end, I felt it was definitely a learning experience and will do the same if I see someone with a similar interest.
It's fun to stroll down memory lane with hifi. Hope people pipe in with some good experiences.