As I re-read my post with fresh eyes this morning, it struck me that I may have come across as ungrateful. I am certainly not! I adore this site, and I'm indebted to everyone who makes it happen, from the buyers to the scanners to the editors to the uploaders to the coders to the staff. I'm just offering my perspective as a user. Moreover, in the real world I work as a processes improvement project manager, so I'm rarely content with how things are, when I can imagine how things could be. And I stubbornly refuse to accept the idea that things ought not change sake of appealing to the phrase "that's how they've always been"!
That said, I really don't think things are as complicated as you suggest. Yes, there are exceptions. And if you try to build your rules around those exceptions - those few odd books, or those few picky users - you'll give yourself a headache. It's easier to let them be what they are - exceptions to the rule.
I refer again to some torrent trackers I belong to (all of which are also run by volunteers). One in particular hosts 1.2 million torrents. Rules are in place about those uploads - what type of file they can be, how the files are named, what folder structure is used - and by golly, it works! All 1.2 million files conform to the rules.
You do make a good point that most files that might be uploaded here have already been uploaded here, and that going back and changing them would be a chore. You also suggest that things might be done differently if you were to start over from scratch. Why not consider that? This site is great as a massive, lightly-organized dump of scans, but with some thoughtful curation work, it could become a truly amazing archive of history - a "museum" in the truest sense of the word.
Anyway, I need to get back to cataloging my own collection. Let me know if you ever feel like starting fresh, I would love to help.