Reluctant to wake a sleeping thread, but after having six full days and change on the new system...
First, going with a "retina" type display was unquestionably the right thing to do, for me, at any price. The first couple of hours, the smaller UI (fonts, etc.) made it a little hard to feel focussed on the display as I configured the system and populated it. A 12-point typeface is about 15% smaller on the XDR than my Apple LED Cinema sitting next to it. The next morning I was already over it, didn't really notice unless I looked at the Cinema next to it. But with everything rendered at twice the resolution on top of that, the crispness of XDR is stunning next to the old system. Though smaller, it's so much sharper that it's easier on the eyes. I'm significantly nearsighted but try to wear no correction at the monitor so it doesn't get worse (it's from living in front of a computer monitor for decades, of course).
My vision is better with the XDR, the eyes aren't struggling to bring into focus something that is not quite in focus (any anti-aliased text on a non-retina display). I have no doubt this will be a huge win for my vision, long term. So, as for the issue of going with higher resolution versus ultra wide and other non-retina options, I'll never question that move for a nano-second.
The other issue of what size—again I was looking for a "roughly 2x" resolution monitor, displaying something near the UI size of my old system at double the res. That pretty much means 24" 4K, 27" 5K, or 32" 6K. Wasn't interested in staying with 24", even with multiple monitors, I wanted at least one screen significantly larger than my old ones. That pretty much meant the Apple XDR or LG UltraFine 5K. (The Dell 8K was another possibility, other considerations.) I wanted a significant move up in screen real estate, I went with the XDR. I was apprehensive, maybe the 5K would big enough, maybe the 6K awkwardly big—I couldn't audition them due to the shutdown. So I gambled big by going XDR, but I'm happy with the decision. I think I would have wished for more if I'd gone with the 27" 5K—the 32" 6K is large but not overwhelming, I like the size.
One unexpected thing that I'm thinking now is that I'm so happy with the XDR as a main monitor, I might be OK with one or two 24" 4K monitors as side monitors, which are very cheap and plentiful. I think if I'd gone with the LG 5K, I'd want at least two if not three, so it would help mitigate the cost difference a bit if I'm content with smaller 4Ks for the sides.