The Dropbox folder functions in most respects like any other folder on your Mac. So, from Accordance, choose File>Open and then navigate to their location in Dropbox.
For example, I have A folder Structure for the lectionary (series of weekly readings) I use, with separate folders for each Sunday. I save a variety of documents in each folder, including a workspace. So to access my workspace for tomorrow's service, I would navigate to Dropbox>Narrative Lectionary>Year 4>11-10-2013, and open the workspace in that folder.
Does that make sense?
In other words, you don't have to save workspaces to User/Accordance Files/Workspaces. You can save them in any folder on your Mac, or in Dropbox that you chose.