Trouble is knowing when to stop.
I've spent the past three months re-writing and editing to deal with all the comments of people I asked to review the second draft........there comes a point, i think, where you have to say 'this is it' let's see how it flies now.
That is very true. In fact, I would go further and say that at some point making major changes can hurt the manuscript. I certainly have a too-much-tinkering rule.
But, there are edits, and there are edits. Which is to say, there is editing for story, plot, characterization, etc. And there is editing for grammar, spelling, word choice, etc.
While you can certainly do too much editing for story, plot and characterization, it's tough to do too much editing for grammar, spelling, and word choice.
So, you might take a couple of specific things, perhaps basic things, and make a pass through the manuscript looking for them. I sometimes do this when I want to target something specific like:
Adverbs. Every occurrence of an adverb is an opportunity for a better verb.
That is, of course, pretty basic, but you might take a few basic points and go through the manuscript looking for them. It's sometimes hard to catch everything when you are looking for everything.
I also take targeted passes with more difficult concepts such a dialogue pacing, point of view depth, etc. But I tend to concentrate only on one of those as opposed to rounding together multiple smaller things to look at.
Anyway, that would be my suggestion if you are anxious to tinker. I think most writers have a few bad habits, so if you know what yours are you can do a concentrated pass looking for them.