What makes a manuscript "polished" is (beyond the obvious stuff like "free of typos and spelling/grammar mistakes") pretty subjective. There have been times readers have responded to my early drafts with, "wow, this is already so polished I can't find anything to crit" and other times when they've responded to draft 50 with "this feels like a first draft...am I right?"
There've been times where I've read published novels that I absolutely loved, that felt flawless, and then heard an editor or reviewer calling them turgid and bloated and saying that whoever edited this must have been asleep at the wheel.
There are other times I've read a beloved classic and thought that it read like an early draft. I had this thought about TKAM, to be honest; large sections of the beginning chapters are just really slow and info-dumpy, and there are whole scenes that feel like they could be cut without affecting the plot. At the same time, I recognize that a lot of the stuff that I found boring, others would find charming. All those little details about the town and the day-to-day lives of the townsfolk are (for many people) what give the book its character and soul, and given that it's about a slower, more gently paced time, the lazily ambling pace is kind of fitting.
So, yeah, it's hard to say when a book is ready to go. There's no such thing as perfection; there will always be things to improve. At some point you just have to draw a line and say, "Okay, this is done."