Do you play with your bass fairly low? I ask because I'm (literally) legally blind and can still see them, but I also play with my bass pretty high up. If it was hung lower, I probably couldn't.
Perhaps lower than you, but my vision is poor, and I am typically backing vocalists who have the light. I tried a friend's lined fretless Jazz and lined Skyline 55-01 a few times. They were fine, but I couldn't see the lines very well—or much at all really.
I play upright and unlined fretless, so my only real interest in the Jazz and Skyline were to try different sounding basses. I used a '71 fretless P-bass as my main gigging bass for five years—and from time to time gig a lot on upright. I was classically trained, so I guess that seeing the lines never really mattered to me.
Heck I can't really see the side position markers very well, either. I usually don't wear my "short range" glasses when I play, and if I wear any glasses, it is my "driving glasses (prescription sunglasses)," so I can see Cues from other players.
I honestly can't see very well up close without a lot of correction. While I am not legally blind, I am 63, and find I can't manage bifocals. In addition, I have mild cataracts, which are really a problem when there is a combination of darkness and glare from stage lights.
So, my observation that I "can't see the lines, why bother with them," comes from an upright/fretless player who can't see the lines. Probably not relevant to many players.
However, I teach double bass to kids, and find that they do just fine without lines, too, and their eyes are quite sharp.
