Debi Alper and I have just finished teaching our online course in Self-Editing Your Novel (a new one starts in January), and one of the questions that came up as everyone collapsed in a heap after six weeks of learning how to re-vision, re-visit, re-vise, re-write and sometimes re-build their novel was, "When do you stop?" When do you say, "That's it," and send it out, or put it away for some months, or give up and start the next thing?
I blogged ages ago about the rather but not totally erroneous idea that it's possible to "edit out the freshness", and I often link to my blog about not fiddling. With anything the size of a novel you could always change bits, and yet in the end you do have to stop. So there isn't a clear answer. (I always hesitate to provide answers, because it feels a bit arrogant: I'd much rather ask questions for you to come up with an answer.) But if you want one, then the blog on Not Fiddling provides a clue; if you get your mind clear about what you're trying to do to the story today, this week, this iteration, you'll know when you've done it to the best of your ability. And when you've done it, and re-read the whole result, and come up with a new list of jobs, and done them, and rinsed and repeated till you're down to typos, then I'd suggest it's time to stop. There will be four trivial typos, one hilarious one, and one hideous continuity error you won't spot till a reader points it out, but in 100,000 words that's okay, and they won't break a deal you would otherwise have made.
For many writers it's much easier to go on fiddling and picking at it, getting more feedback - and perhaps genuinely making little bits of better in lots of little places - than to stand back, think structurally, confront the big engineering. And it's much, much easier for some to keep doing either large or small revisions, than actually send the beast out to be judged by editors and agents and reviewers. Yet just as many writers stop too soon, either from ignorance of how much better the novel can and must be for revisions, or because they're bad at coping with delayed gratification and can't wait to get their work out there ... even if that gratification is the deeply equivocal business of submitting your writing to the industry's judgement.
So the not-clarity of the answer is partly because "When do you stop?" is actually two questions: revising is partly about making THIS piece better, but it's also about learning to be a better writer. Every time you spot a word or phrase or sentence or paragraph or chapter which could be better, and don't just move on, but set about trying to work out why and how, you're becoming a better reader-writer. It's the equivalent of the fact that every time you run for a bus you're not only trying not to be late for this particular party, you're also giving your cardiovascular system and bone density a bit of a workout for the future. You might miss the bus but it's still worth doing, for the second reason.
In other words, it's not just that most of writing is in the re-writing, it's also that most of learning is. But there is always a limit on that learning, in the sense that there are things you need to learn, which this project just doesn't involve. However often you run for the bus you won't get better at climbing trees, although the cardio fitness will help in a general way.
So maybe one part of the answer can be found by asking "What will I learn if I go on revising this?" versus "What will I learn if I send it out now?" Which is more use to you?