I used to attach a lot of importance to having lots of frets on my basses, with access all the way up the fretboard, and my high-end basses are all 24-fretters with big cutaways to get at 'em. But the reality is that the longer I've played bass, the *less* often I end up doing anything above the 19th fret, usually for the high voices of chords and arpeggios.
I'm definitely partial to through-neck basses, but it's not because they necessarily have better high fretboard access, but because of what the greater rigidity does for tone and sustain.