Everything except the money changing on your list could be achieved without the Euro.

I was a remainer and I'd love to rejoin and Schengen, the mobile roaming stuff, etc. are all wonderful and I would like them back.

I'm not convinced the Euro would be a good idea and I'm absolutely convinced that you'd lose public support for rejoining if you tried to go that route.

I keep wondering if EEA + Schengen would be a viable middle ground.

What year was this? The removal of a lot of this financial friction was coming to and end regardless of the Euro or ECB. Didn't Croatia only join the Euro this year? I'm finding it hard to believe this archaic mechanism existed up until Jan 2023, that is to say I find the example slightly disingenuous.

The friction between Ireland and the UK is near zero, both have different currencies.

This isn't to say there aren't benefits to the Euro; on an individual level of course not thinking about exchanging or exchange rates makes life easy. It's simply not palatable to the UK, Brits or the core financial institutions by which its service oriented economy excels.

To play devil’s advocate, a lot of that is now ameliorated by the decline of cash and the rise of certain neobanks. I’m in Denmark at the moment, and thanks to my banks (N26, Revolut), I can cheaply convert my savings (EUR) and spend in the local currency (DKK); either at transaction time (N26 and Revolut), or ahead of time (Revolut) all with minimal fees.

The only country which benefited from the Euro is Germany and they had the audacity to not only refuse the fiscal policies and transfers which might have made that fair but actually undermine the most affected countries like Greece even more. I personally lost all hope for the union after the debt crisis and considering the state of politics and denial of reality in the north of Europe, I really wish we would just leave too. I’m sad we lost the open border with the UK however, genuinely love the country but I’m not sure the rest of the EU is worth it.

No borders on the continent is useful, but not sure what it has to do with currency.

Nowadays when I travel, I just pay with my usual bank or credit card and get good rates without thinking about it. If my bank didn't have good rates, there's Revolut.

The main pain is that the EU hasn't standardised payment systems. So in parts of NL and Germany, you might find your Visa isn't accepted because they only take Maestro, or, in Sweden, Swish, for example.