chessnut,
Your approach is using a low "bits of entropy" passphrase, and then obfuscating it with a deterministic algorithm (in your case hashing keys). While it is unlikely that anyone will discover your secret any time soon, when bitcoin becomes more valuable there will be more "obfuscation algorithms" being checked automatically on low entropy passphrases. And laying out your general approach makes it easier to generate such algorithms. If you want to use brainwallets, spend the time to generate and memorize a truly random "high bits of entropy" passphrase. My recommendation is to use diceware.