I'm no artist but having lived through every domestic video format here's a brief summary of what i know.
There are lots of ways of screwing up an analogue video signal. Capture, storage, transmission, and display all create unique anomalies that cant be recreated elsewhere in the signal chain.
All CCD cameras are digital, and all late era VCR's have time base correctors, noise reduction, colour correction that digitaly process the picture
Older equipment relied far less on servos and pll's and more on manual controls, so there are tons more potentiometer adjustment points for screwing up or enhancing the signal.
Tube based cameras, vidicon etc had a totally different "look" to later CCD cameras. They saturated and smeared with bright lights and the tube rattled to the beat when exposed to loud music.
If you have ever tried extracting a mangled tape out of a VCR, you will know difficult it is to do anything with the tape in it's shell.
Track down some of the early 70's AKAI and SONY, Panasonic open reel video recorders. These are similar scanning head devices to cassette based VCRs but the tape and heads are exposed. (Not to be mistaken with the broadcast 1" and C formats, whose machines were the size of refrigerators).
I have an AKAI VT100, from 1968, and the later colour VT150, They are pretty easy to keep running; but even when perfectly calibrated, the picture qualiy is still "shite" by modern standards.
Cable lengths, cable types, and over the air links all affected the way things looked, so there's a lot of room for experimentation there.
I dont know if anything i've written constitutes as circuit bending, but one man's art is the maintenance tech's brain ache; or something like that.
Good luck
Hywel