It would still make a significant difference since someone could still compromise your Dropbox account... Having a password manager doesn't all of the sudden make all of your passwords secure on all of your different accounts.
I suppose there are cases where someone got the dropbox password hashes and didn't own dropbox enough to have access to your dropbox account without reversing your hash. However, in most cases where plaintext passwords are exposed, the attacker will own your account at the service that was attacked because they are already inside that system.
If the DropBox passwords are leaked I am going to change my DropBox password whether it was hashed properly or not. The difference is that I won't have to change my password on dozens of other sites.
Plus 1Password has a sort of watchtower setting which shows you which websites had know security issues since your last password change, so you can stay relatively secure all over the place.