You should both distribute your file you want to keep to several devices, as well as a service who's job it is to back things up.
Dropbox is only the former.
I have a backup on a USB, but updating that daily is a hassle hence why I used DropBox- their added 2 step auth was also a big bonus, but if I lose that file I'll have a hard time getting my passwords back..
As jpadvo said, I might look into making some one way backups to S3 or something.
Buy a time capsule and back it up locally or get a subscription to something like crash plan pro.