I was previously a maintainer of certain Debian packages, and of similar vintage, so this advice comes with the extra salt of having seen how the sausage is made. I shudder to think how many abandoned files, orphan packages, and obsolete/bad-practice configurations might be lurking in a system that has only been release-upgraded for decades. Yes, no doubt it functions. By the same token, people can live in their own filth. Should they? I choose not to.

That said, I may do a speculative dist-upgrade on a snapshot to reveal & prepare for conflicted conffiles in advance, but I'll throw that away, I won't rely on the merged result across a release upgrade.

But when there's a configuration change dpkg-configure asks you if you want the upstream one, no?

Debian releases are somewhat slower than Ubuntu or similar - given infinite time, esoteric configurations will break on update due to some edge case 4 dist-upgrades ago.