I'm sure I will be corrected, but I actually believe that 95% or more of the readers of this forum. are amateurs who intend to remain that way.
Those thusly put off will be happy to know that some of the best musicians in the world do not play scales, as such! What they do, is to practice interesting scale like passages from pieces they are learning, or from their repertoire.
The idea is to play "these scale like" passages slowly and carefully a couple of times as a warm up. Then when you get to the piece in your practice routine, that passage will be a little easier.
As a matter of fact slow practice is a lot like slow food. It is more enjoyable and actually is the trick to playing rapidly. Just relax and listen to the music you are making.
Don't worry too much about expression, it will come through all by itself as you play. All the tricks in the world can't hide a boring person"s playing!
A lot of good points in this posting, in my opinion!
I share your assessment that most of us here are amateurs. However, amateurs and professionals have one thing in common: they want to play as well as they can, given the time, talent and resources at their disposal. Professionals play for money and recognition, amateurs play for personal satisfaction. These are equally strong motivators, to my mind.
Yes, we must realise that "practising scales" is not just playing "doh, re, mi, fa, so, la, ti, doh'" and back down again. When I was learning to sing, my teacher had me sing broken scales like "doh, mi, re, fa, mi, so, fa, la, so, ti, la, re', doh'". Or "doh, re, doh, mi, doh, fa, doh, so, doh, la, doh, ti, doh, doh', doh" (try that one along the rows of your anglo - you may discover some interesting alternative fingerings!)
These are the "scale-like passages" you wrote about, and they can be used to practise phrasing, too (e.g. "DOH-mi, RE-fa, MI-so ..."). you can give the notes different time values; you can do the whole exercise in 3/4 time or 4/4 time; you can build up the volume and take it down again, etc.
If you then put a chord under each note (or phrase) of the exercise (probably easiest on an anglo), you've got a pretty little etude, which does not have to be boring, but still gets your ear and fingers accustomed to finding all the right notes and the appropriate chords.
Make up words to it, if you like. Even if you only sing them mentally, they will help to shape the music.
I've heard top-class musicians recommend slow practice, too. If you always play fast passages up to speed, your brain tends to delegate them to the fingers, and if the fingers get knotted, the brain no longer knows what to do, and you crash out. Playing slowly, concentrating on each note, keeps you in charge of affairs.
And yes, expression is not a matter of skill or tricks or neat fingerings. Skill has to do with producing the right notes in the right sequence. This is instrument-specific. Expression has to do with the music itself - with finding the coherent phrases and making them audible by accentuating the appropriate notes and glossing over others (using your instrument-specific skills, of course). This is something that a musician can transfer from his first instrument to a subsequently learned instrument. And remember, the first instrument that most of us learn is The Voice! A pretty good guideline to expressive phrasing is to sing the passage through, and then try to play it like that.
Whether you do all this for four hours a day, like a pro, or for ten minutes each evening, like an amateur, is to my mind only a matter of degree.
A famous French Impressionist painter once said that the secret of being a good painter was never to let a day pass without putting pencil to paper at least once. By analogy, even the amateur concertinist with a demanding day job can usually find the time (say, 5 minutes, including unpacking and repacking the concertina) to run through one of those "scale-like passages", just to remind his fingers of where the notes are. I've done this with difficult passages in tunes I've been learning - notably that descending scale passage in "The Sailor's Hornpipe" - and it works wonders!