You really can edit/revise too much. At some point you just have to cross your fingers and send the book out. It's like if you go out to eat and you're done, but you still have some left. If the waiter doesn't come pick up your plate, you keep picking even though you're full. Then you have regrets. Ok, so maybe it's not exactly like that, but it's a little.
The problem with changing something, especially in a query letter, is what you had might have worked with Agent A and now won't and what you originally had might have sent them to the moon.
I've read my own book at least four times and found mistakes and/or made changes each time. Now aside from the typos or any plot inconsistencies, who's to say I didn't change something good to something just ok?
Ultimately you, the writer, have to say--I love this book, I think it's great, and they will too. Never tell yourself that "they" won't like it, never pick on yourself, because there are plenty of people more than willing to do that for you. You wrote a flippin book for crying out loud, how many people can say that? Not as many as you think, considering how many people there are on this planet.
If you're lucky you'll have people you trust who will read your book and tell you what they think, good or bad. I've only had two people read mine, one thought it was really good and so did the other, but with a few "buts".
My biggest problem has been sending queries too soon. Because the query wasn't good enough. I think I've perfected it now, but I'll just have to see if "they" like it.
Bottom line is, ask for help or a critique, but ultimately you just have to trust your instincts and cross your fingers.