Joey,
It's not about being smart enough, just a matter of listening and feeling.
Yeah, it takes a while - quite a few years for me, having come from a guitar background - and about all I'll say about my current ability is that a very small number of people have heard me play and don't get too irritated by it :-)
As to the lines, I commented a while ago (some oher thread, but it could be found...) that I personally find lines to be distracting. I think that to play fretless well (or upright, whatever), you have to position your fingers by ear, rather than sight.
I don't mean that to sound snobbish, and I do sometimes look at my side dots, and if I usually played fretted then I might really appreciate the lines. But I also just love the look of a 'blank' fingerboard, and wouldn't have it any other way.
Maybe you're right about the DNA... I have a really hard time playing a fretted instrument these days, and a big part of that is just visual, seeing all these pieces of metal where I think my fingers should be.
It's a personal choice, and that's just mine.
I think you should go for it, Joey - find a used one, don't spend a ton of money, don't judge yourself, and just have some fun for a while. (Maybe that's not exactly what you were asking, but it's a good answer.)
-Bob