I totally agree with you. That's why I downloaded the service manual for the AK 550 some months ago.
You do know there is a word for that "something" you mention. Is that word in the language filter?
There is one thing you forgot to mention in your list... Parts availability.
Personally I don't really need ready access down the street for any parts for any bike I buy. Just if I can get what I need from... someplace.
My very first bike was Harley Davidson 125 dual sport (actually produced by some Italian company and distributed by AMF). I bought that bike about 10+ years after production had stopped for it. The throttle controls casing broke and I had to push for HD to cast me a new one. Actually surprised they did that but that's what I was told. It was cast aluminum, very brittle. This was also the bike I learned what it meant to own a Harley. The piston had seized and badly scored the cylinder. Spent the Winter months in my one car garage in pieces all over the floor. Re-bored the cylinder double over-sized, replaced the piston with a slightly larger one and replaced the rings. I think that ended up being closer to a 130 cc when I was done with it.
So valve checks are easy as long as I can get to them without totally removing the engine. Any other maintenance I can do as indicated above. Yet I'm a computer tech, but mainly computer hardware tech much more than the OS or other software. Though I can do both and did while in the Navy and ANG as well as my civilian career. It does help to be mechanically inclined also. I sometimes take things apart, repair, and reassemble without the help of manuals. Did that with the Harley. I find it's really not that hard but it is a matter of deciding that you can do it.