But then you come back to the problem of choosing the secure password, don't you?
Which brings you back to the point that you need to learn about choosing secure passwords.
Ah ha, but no-- the requirements for the password security are much lower.
With a brainwallet, the moment you use it everyone in the world can begin cracking it-- in parallel with all other keys they are cracking at no extra cost. They can also apply precomputed rainbow tables to try may of the passwords they tested in the past against it-- at low cost. They also can see the bounty attached to it.
If a wallet is encrypted it has a salt and (hopefully) an expensive KDF. The attacker cannot attack multiple files in parallel. If the whole wallet is encrypted, they don't know what their payoff will be and most importantly they can't even begin cracking until they get the file. The security becomes multi-factor: You must have the file and the passphrase. Theft of the file may also be noticed, giving you time to react.
So if your passphrase is a little weaker than you intended it to be-- there is likely no great harm.