So I've actually never cared much for release parties. I think because by that point the work is 'done', and I'm ready to move on. Plus, if upper management is involved, it feels very parasitical ("let me attach myself to this launch"), and if they aren't it feels unnecessary (we know we did a good job). And the timing is always problematic; if it's literally as we release it feels disingenuous just knowing that if anything goes wrong the team has to step away from any sort of party (but not upper management, or others who glommed on), and if it's after the fact I've mentally moved on.
That said, all the other things are must haves, not just because of morale but because of effectiveness. Things don't get done without definitions of done, things don't get proper feedback and iteration without demos, etc.
From your story, you seem to have very different "release parties" than what I have encountered.
The ones I'm talking about are ranging from "buy some nice beers and munchies and drink one in the office" to "hire a boat, bring a radio" to "have dinner together". Basically a friendly, shoulderpatting event amongst peers.
*Edit: obviously all pre-covid lockdowns and work-from-home.
So that just sounds like a team event, which I try to do once a month just to help keep the team connected.
I think the difference is internal vs external release then. Our internal releases were generally "nice job" and the like, as we completed sprints. It was still a clear recognition of something being completed. The actual external facing launch that the company cared about, the 'go live', was more what I was referring to, and which never really meant much, to me at least.
That said, all the other things are must haves, not just because of morale but because of effectiveness. Things don't get done without definitions of done, things don't get proper feedback and iteration without demos, etc.