While I appreciate the clarification, the need to have a separate account for each vault is still ridiculous. Looking at my 1Password, I currently have 20 different vaults set up and I expect that to continue to increase over time. The idea that I would need to make and maintain 20+ different dropbox accounts for each vault is flat out unacceptable.
To my knowledge, every one of the cloud providers you support is capable of sharing individual subfolders within a given account. If you had, at a minimum, separated the vaults into individual subfolders, then that would still have been fine. This is how 1password does it, for example.
Password management needs to be as effortless as possible, and the way multiple vaults have been currently implemented places an absurd and unnecessary burden upon users. I will be sticking with 1Password for now.