I'm doing the same thing, I have over 100 domains, and dropping all of them that come due that aren't producing. I still have 3 or 4 I've never put anything on yet, bought them with plans to create something on them. One of them auto renewed the other month and it was like, crap I could have let that go, lol.
$600 checks are cool, I was getting those from CCBill until I lost rank in the last update.
Now I'm lucky I get 1/2 of that a week.