[jaredklewis]

How is brute-forcing a concern?

Your password might be a guessed in a dictionary attack if you have a weak password. Or if at some future date a KeePass specific vulnerability is discovered, someone might be able to use that.

But someone trying to brute-force your password isn't a problem anyone needs to worry about.

To my mind, the real downside to using dropbox to store encrypted stuff is that the existence of the encrypted stuff is not a secret. And recently it seems the spooks look upon encryption with ever increasing suspicion.