> So far my impression is that there are a whole lot of other things I need to worry about in Postgres before I spend time considering serial vs. random UUID vs. ordered UUID. Am I wrong here and this is something that really matters and you should invest more time in?

Like any sort of optimization I believe this will depend on your workload and what's important.

For me when I switched to UUIDv7 a few months ago, it was basically no effort to switch v4 to v7 on a relatively new system. I was observing much higher batch insertion latencies than I expected, and producing inserts that touch less of the btree on an index created a very noticeable reduction in insertion latencies. But my workloads and latencies may look nothing like yours. On amazon RDS instances with EBS volumes and relatively low memory, insertion latency stood out, so using strategies that reduce the number of disk blocks that are needed has an outsized performance impact.

This of course would produce different results on different hardware / system sizing.