Flew JFK-ICN-SIN and back last month in Y and didn't feel that things were any worse than they used to be. Re your observations:

FAs: Not all of them were "warm and welcoming" (service tended to be on the cold/clinical side) but there were several who definitely still were (especially on JFK-ICN-JFK). But then again might have been a language barrier thing (since I don't speak Korean).

Coat: Never noticed that but then again it's nearly summer in the Northern hemisphere and I don't think anyone had them on.

Food quality: Western option ICN-JFK was rather odd (a huge piece of chicken breast in some unidentifiable sauce) however all the Korean meals were very good (had bibimbap on 3 of 4 flights and didn't get tired of it lol). Catering ex-JFK was surprisingly good. Your issues with the food might just have been a SYD/outstation thing?

Menus: Never got a menu on any sector but didn't receive any menus on my flights in 2015 either.

Greeting: Never got one but wasn't expecting one to begin with.

Toothbrushes: I always felt that throwing away the half-used mini tube was a waste anyway so this is probably a change for the better

That being said OZ is still miles ahead of UA and definitely still on par with/better than NH so I don't think their service is an issue or that things have deteriorated since a few years ago.