Not sure what the advantage is.
Dropbox keeps historical versions of your files. My concern is that, if an adversary can get multiple versions of my Keepass file which they know are a sequence with small changes between them, then they are much more likely to be able to devise an attack. I haven't looked into this any deeper yet.
I've been working on my net security as well and I've had a hard time compromising security vs convenience and fault tolerance. My situation is made a little more complicated because I don't have a smartphone which rules out mobile based key vaults.
I want a minimal set of dependencies to access necessary accounts, like my gmail. No file I can lose, or password I might forget. I've decided to rely on an ok password and google's two factor auth.
Less important accounts are stored in keepass protected by a key file and password, but I'm worried about losing the key or vault file.
I am putting a lot of faith in the security of KeyPass, as I don't put a lot of faith in DropBox to keep the file secret. If DropBox's sync system wasn't so simple/unobtrusive I'd use something else.
Then as a last step measure, there are backups of the keepass file in case a machine or dropbox have issues.
Perhaps consider using Bittorrent Sync[1] for synchronisation.
For practical purposes, it's similar to using DropBox, the key difference being that instead of syncing with DropBox in the cloud, you are syncing folders across hardware you control. The hardware could be different computers, phones, tablets etc.
As an extra safeguard for KeePass, I use a key file in addition to the password. The key file I also keep in cloud storage (in case any of my machines die in a fire), but on a different cloud storage provider. That way I can always reconstruct my password environment, but it would require compromising two cloud stores and keylogging my password to open the safe. (Or access to one of my local machines and a keylogger, but in that case I'd be hosed anyway.)