If I made 2/3 of what I do now, I'd be pretty much as happy as I am now, and want more money; if I made 3/2 of what I do now, I'd also be pretty much as happy as I am now, and want more money.

You're burying your argument in the constants 'pretty much' there. You can repeat your argument sorites-style after you have taken the 2/3 salary cut: "Well, if I made 2/3 what I do now, I'd still be 'pretty much as happy' as I am now" and so on and so forth until you have hit sub-poverty wages.

To keep the limits of the log argument in mind, log 50k is 10.8 and log (50k+70k) is 11.69 and log 1 billion is 20.7; do you really think if someone handed you a billion dollars and you filled your world-famous days competing with Musk to reach Mars or something insanely awesome like that, you would only be twice as happy as when you were a low-status scrub-monkey making 50k?

(particularly when progressive taxation is factored in).

Here again more work is necessary. One of the chief suggestions of positive psychology is donating more and buying more fuzzies... and guess what is favored by progressive taxation? Donating.

The logical conclusion is that I should lower the weight of salary increases in decisions, the opposite of the conclusion proposed here.

Of course there are people who are surely making the mistake of over-valuing salaries; but you're going to need to do more work to show you're one of them.