I completely agree that incrementally ratcheting up the metronome is not the best way to get faster. Here's what I do instead. Lately, I've been trying to increase my scale speed from 120 bpm to 150 bpm (1 click per quarter note, scales in sixteenth notes). I do not find it helpful to work up a few bpm at a time. In fact, the gradual increase in the pulse makes me anxious and tense and makes it harder, even at relatively low speeds. Instead I do the whole scale without metronome using quick finger staccato; then do it in lots of rhythms, 2 rhythms (long-short-long-short) through 6 rhythms (long-short-short-short-short-short) doing every permutation of each rhythm (e.g. long-short-short; short-long-short; short-short-long) which is equivalent to starting the scale on each of the first X notes for the X rhythms). When doing that, I try to play the group of short notes at the target speed, but without the metronome.
Then I set the metronome 20 bpm above my target, so 170, in this case, and play 9 note fragments of the scale at that tempo - 9 note fragments let me start and end on a click so I can be sure my tempo is right. At first this is really hard (remember I'm starting from having played the scales at no more than 120 bpm). But I just keep going for it, until I can get 9 note fragments sounding clean at 170 bpm. Then I slow the metronome down to 150 and try to play the scale. If I get it, I repeat it a few times and then back the metronome down to 135 and play it at that (now easier) tempo 5-6 times through. If I don't get it (at 150), I slow way down, and just run through it at 125 bpm or so and wait until the next day
By jumping around like that, I avoid the gradual increase in tension from ratcheting up the metronome. I also think it helps because playing a very fast scale feels quite different than a moderately fast one. There's a lightness in the fingers and a quickness in getting off the keys that you don't use at slower speeds. I think it's almost impossible to get the right feeling or movements by slowly increasing your speed. Just like if you're a baritone, you can't learn to sing up in the tenor range by singing just a little tiny bit higher each day - you have to learn what it feels like to sing in a connected head voice, which is a different mechanism and feels different than singing in a baritone chest voice, and so you have to get up into that high range all at once, and at first it feels really ugly and awkward. Likewise I think you have to accustom yourself to playing fast in very short bursts and let your bod figure out what it needs to do to make that work, and then just go for it at a much higher tempo than you were playing before.