Interesting discussion, indeed.
My background is on trombone, on which players work hard to develop technique and strength to extend their range in both directions, especially the high end. The notion of being able to simply "buy"extra range is mind-boggling! My own attraction to 24-fret 5-string instruments is probably rooted in that simple fact. I guess the logical outcome here would be 6 or more strings, but I'm not so sold on the timbre of a C-string, and have been daunted by the muting and left-hand reach issues (I have average-sized hands), although as i get more technique perhaps the muting needn't be so much of a problem.
I've played covers in the past, but they are not part of my current scene. Even if in a cover situation, I think it would be cool to drop into that lower register, and there certainly is the ability to use different positions/patterns. But I also dig having a wider range of places to play the same notes - I like being able to get a fatter timbre by playing higher frets on lower strings, than would be an option on a 4. BTW, this is where the Sadowskys kill, because the B string is quite usable for the notes I can reasonably grab on it (not really beyond the 15th fret, but totally loving how the Sadowsky 5-24 keeps it together where I do play - lots of lesser instruments get weird beyond the 8th fret, or don't speak clearly into the low end).
When comping in a jazz context, I love being able to bounce chords and triple stops off of that B-string; some major convenience and flexibility there. When soloing, I'm again digging that flexibility and range of options, both for placement/convenience, and for deliberate timbre choices.
Then consider the question of 4-string familiarity. I've played bass on and off, largely as a goof, since the late '70's, but have gone 4-5 years at a time, several times, without touching the instrument. Once I started getting more serious, round about 2006, I wrestled back and forth, with several false starts on 5-string, but ultimately decided to give it a few months where I'd just play 5. That was several years ago, and I'm not looking back...but I totally get how a serious four-string player, with a whole lot of muscle memory and experience, would have trouble adjusting to 5...I didn't find it easy at first, as a piker.
I've been briefly exposed to D-tuners and understand why folks would dig them, but for me just bringing the extra string works a whole lot better. And again, I'm not rocking out such that extra weight or the "look" is an issue in any way.
De-tuning is a whole different kettle of fish - I totally get why folks may go for the differences in range/timbre/stringfeel that come from going that route. My mind was blown when I first heard D'Angelo's Voodoo album, and I get that detuning has been used from metal to gospel. But I'm often doing things where folks are playing unfamiliar material, with guitarists (and sometimes me) checking out hand placement to confirm the key or changes, so I'm so far disinclined to detune, although reading that Nathan Watts detunes to E-flat certainly got my attention - I LOVE his playing.
Anyhow, at this point, I am 98% of the way toward selling my two remaining 4-string basses - I'm simply not using them, and am loving the 5-string lifestyle. But no reason to be doctrinaire here - let a thousand flowers bloom...it's all good!
