When I upgraded it was an easy choice - double the sensor resolution, better sensitivity, low light handling, rear screen, etc.

I don't remember if I was aware or placed much import on the depth of field benefits from the bigger sensor, but of course shots like those tits would be less impressive without it.

On the other hand, for well-exposed landscape shots the sensor is less significant.

I think I'm more so trying to talk myself out of doing it.

I can see lots of benefits, but the drawbacks are...
Cost - significant, but would hope to last me 5+ years before I feel the need to even consider looking for a new camera.

Size - the reason I bought the A6000 was because I stopped enjoying taking my K200D out with me as it was too big and bulky. But when I didn't I then regretted not having it. So I went for a mirrorless APS-C camera. Going full frame (even mirrorless) pushes me back towards a larger camera. Though I am much more enjoying photography again these days so I'd hope I'd get past the size.

Yeah, I'd say size is something you get past - though I did get myself a decent compact to always carry around for similar reasons, but having the choice I find I don't use it as much as I might have. Still enough that I'm glad I have it, but without it I'd regret shots that I otherwise decide are not worth taking. I always take the D750 when I know I'm going to be doing photography.

I do think in your position I probably would wait a year or two for the next generation before upgrading, (unless you're specifically hitting the boundaries that the A7iii definitely overcomes).