[owensmartin]

I'd like to tack on another key feature to these 13th chords (no pun intended)-- and that is of spreading out the voicing across the instrument's (usually piano's) range.

There's a sort of rule of thumb in jazz that the only interval that sounds genuinely BAD is the flat 9. Try it on your piano right now (say, C and C# an octave up). Notice that a similar interval, the major 7 (C and B) sounds pretty, even though the notes are kinda clashing because they're so close. But on the other hand the flat 9 sounds GREAT if you voice it right. To see this, hit a low C, then E, B-flat, and D-flat. Similarly this chord works with all the other color tones: 9s, 11s, 13s.

I think ultimately what makes jazz piano truly musical is when the musician has spent a lot of time trying out different voicings, spreading them out or crunching them in, and listened to each one to see which sounds the best.