There's a lot of enjoyment to be had actually using these retro systems. A large part of it is nostalgia, I wont deny that. But the way those systems directly interfaced with the hardware does bring some enjoyment too. I think of it like playing vinyl, some people enjoy the colourisation that vinyl adds to the sound but other people enjoy the tactile nature of the medium. Typing your code directly on an Amstrad, BBC Micro or Apple II is a bit like that in that there are technically better ways to do it these days but using the original machines gives you an irrational sense of enjoyment.
I used to explore what happened reading/writing to memory locations connected to the expansion cards on the Apple ][. I later had a Spectravideo PC and one of the first things I did was explore the memory by writing into different locations to see what happened. I also wrote a Z-80 disassembler to try to reverse engineer how much of the system worked (unfortunately, I never got around to properly decoding multi-byte opcodes).
