It might help to make a distinction between 'reading music' and 'sight-reading', which is a separate skill IMO and has different requirements for chart-writing. Number charts are great for sight-reading because they give the optimal amount of information to the player, assuming the song lends itself to number charts. I wouldn't want to see a number chart for "Moment's Notice". Too much information is as hard to decode as too little, so giving a published piano/vocal chart with guitar chord symbols to a bass player is a PITA to sight-read. The job of an arranger is to help the artist conceive of the form and layout of a song as it applies to an ensemble, and expressing it clearly in a score. He gives the score to a copyist who then extracts the parts for the individual players. These days the few copyists who are left use Sibelius or Finale.
My greatest issue these days is that inexperienced people tend to make the notes and chord symbols too small for people with old eyes. I make them as large as I can without making the chart look cluttered, typically 16 pts (minimum!) for text or chord names and 7.5mm for staffs to be sight-read. Most musicians can kvetch about a particular chart for one reason or another, but I've never given charts to horn players without someone pointing out how I could have written the chart better. So do your best and expect complaining.
GREAT points as usual.
One other thing to add, that I probably should've mentioned in the article, is that different instrumentalists expect to see different things.
Clef and key signature on each line is fairly commonplace for string players, but horn or rhythm players don't want to see it. String players have different ideas about ideal music spacing and layout, too... typically they seem much less concerned in my experience with clues to form, and more concerned with immediate readability of each individual bar. For a rhythm chart or even a horn chart, I might sacrifice the latter in favor of the former, but for string players I'd sacrifice the former for the latter.
Also, one area where I'm totally deficient is slurs and bowings for string players. If you right four sixteenth notes with articulations on each note, that's not enough, and that's a mistake I make a lot (fresh in my mind; just recorded six of my string arrangements on Monday). They need to know if they're supposed to be slurred, detaché, etc.
Also, I've tried specifying cutoffs for string players and they just look at me quizzically, whereas EVERY horn player I've ever written for knows what I mean.