I still have my Nikko ND-1000C. With Dolby C, a 3 head deck and proper bias adjustment you could get close to CD quality. The Nikko had an auto-bias feature that recorded and played back test tones, but I got better results with one of the factory settings and the right model of Denon cassette. Back then the tapes were primarily for the Clarion head unit I had my car which also supported Dolby C.
The tapes have certainly degraded over time though. Anything I'm really fond of can usually be found on the net and gets replaced with a digital copy. Jumping to a particular song on tape is still a PITA.