Having watched the last art is fine video I think 32 is going to be mandatory for me in the future as I tend to keep my equipment a long time.
Do you mean the Art is Right Youtube channel? He produces a lot of use cases showing indeed that more memory is better.
And while he does recommend 32GB of RAM for photo professionals, he also notes that there is an alternative ownership strategy that some use:
flip machines at each new generation, buying the base model of each new generation. This may allow for one not to hit some sort of performance ceiling with an old computer.
I like you have a very old Intel iMac. I like to use things for as long as possible (in this case 15 years). I'm not a flipper.
But I too am shopping for a new Mac, and have considered the exact same models as you. I don't do photography currently, though in the past I have done so as an avocation, and sometimes selling images.
So I am considering buying a base-level Mac Mini with M2, then when the M3 comes out to flip it for an M3 Mac Mini, and so forth.
Nice thing about Macs is that they are desired as used computers, though with platform changes (such as from Intel to Apple Silicon) one needs to be aware that old architectures present a problem.
I figure I can sell a used Mac Mini for more than half of what I paid for it. So if I buy a 16GB M2 Mac Mini for $679 (Edu pricing), I should be able to sell it for at least $350, probably $400, a year later. I can probably do this for a few generations, until I am not interested in computers anymore.
The other alternative is to lease the machine (which one can do through Best Buy.) If one has a business (you mentioned you occasionally sell images) the lease cost is of course a business expense.