It happens to nearly every writer. You were convinced your book was as perfect as you could make it so you queried. Then you submitted. Then a few months later you had an epiphany. It wasn’t ready, but revisions fixed it. Now, what do you do about those agents who already rejected?
A quick search of agent Tweets will tell you that every agent has a different answer. I err on the side of, “what’s the worst that can happen.” While other agents say once is enough.
If you are following this blog you will be well into your next book before you even have the epiphany and the real consideration isn’t whether you should query an agent with the same book, but how can you take what you’ve learned from those revisions and put it in your second book.
Once you query your book you should already be writing your next book. In fact, I wouldn’t even start querying until I’ve started writing the next book. Let that first book marinate a bit before sending it out. This allows you time for epiphanies. It also allows time to have the next thing, which is always better than the last thing.
If the revision epiphany still pulls at you it really doesn’t hurt to requery a few of the agents who said no. That being said, you also don’t want to be the guy who keeps querying the same book over and over. That’s not something to be remembered for.
The choice is yours, but if you do decide to query again you better make sure the book is significantly different and not just a few line changes here and there.