For a long time I yearned for 24, just for the sake of having two octaves on each string. Along the way I realized I didn't need them for any kind of playing, only for looks. That kind of insurance is totally lost on me.
I don't know what "need" means, but I like two octaves on each string (especially on a 6) and though I don't use the high frets much, I DO use them! A "truncated" bass to me always feels...well..."truncated". It's a lot like a low B. You don't need it much, when when you need it, you need it.
But that said, I have to add that I've also discovered that 24 fret basses do not seem to have the slapping tone that "truncated" basses do. It must be something about how the string is divided when it hits the end of the fretboard. All my 24 fret bass just seem to have a "thin" slap tone.
