I have a question that may (or may not) fit into this...
I have been wanting to get a fretless for a while and assumed that I should probably get a lined board, since I have no idea if I'd be any good at it.
When I play a fretted bass, I play with my fingers right behind the frets. Would this help (or hurt?) to play an unlined board from the get-go?
Well, I started bass on an upright. I've got both lined and unlined fretless bass guitars. And here's what I know so far:
1. Getting a reference point on a fretless bass guitar is harder than on an upright (Upright has positions that give you reference).
2. The REAL reference points on a fretless are the dots on the SIDE of the neck. BOTH lined and unlined have them!
3. Lined necks are indeed a "crutch" for the noob for two reasons. The first (not so important) is the lines give you reference points at every note not just at certain ones like the dots do. And the second is that because a guitar is held at a side angle unlike an upright there is a tendency to start fingering across the neck at an angle ruining your intonation on the higher strings. Lines remind you not to do that especially when you are practicing and developing your ear! So for that they are an aid for the beginner.
4. But there is a difference between performing and practicing. Performing, you won't be seeing the lines anyway, so they won't matter. If you haven't developed your ear and muscle memory while woodshedding, lines ain't gonna do it on stage.
5. Lined necks have a bad rep because of the perception that they are "cheater" lines that imply the player is a noob. (see above)
6. Lined necks have a bad rap because often entry level bass makers offer a fretless model that is just the fretted model but where they charge more for not bothering to install the frets! Hence it tends to have a rep of a cheap entry level less-than-gigable bass.
[By the way, if you don't know if you'd like/be good at fretless an SX fretless is an excellent way to go. Cheap. Reasonable playability and tone. Lines (natch). And you can get a large percentage of that minimal investment back if fretless is not for you.]
7. Lined necks in my experience make the bass appear to be a fretted instrument. The audience (even some bass players) never seem to notice that your lined neck bass is fretless no matter how many fretless licks you play.
8. Which leaves us with the issue of "look". By all of the above, you can see that if you really wish to "show class" on stage and make a big point of the fact "look, I'm playing a bass with no marks on the neck to tell me where the notes are", then obviously only an blank plank will do the job.
So as it turns out my Alembic 6 is blank. Clearly you can "show class" with that! My SX fretless has lines because...well it actually IS a cheapo entry level hundred dollar bass! And I WISH my G&L L-2500 were blank but it has lines because it was used and that's what the previous owner ordered.
And my Carvin Acoustic fretless has lines because it was my first fretless bass guitar and *I* ordered it that way because like ModuMan I believed that lines would be a help. And as noted above to a small degree they were. But they certainly weren't as big a help as I thought, and you certainly don't need lines to learn to play fretless, and sadly later you discover the issue of lined fretless basses being mistaken for fretted basses on stage. So if "showing class" on stage is important to you, I'd make the effort to learn without lines so the bass will have the right "look" later when you can really play it.