But there is one weak point with your dropbox workaround: you can’t work on the same project file together at the same time. Who saves at last, will overwrite the changes of the others. You need to save different versions then, which you have to put together manually (which is quite easy with the new import from project function!).
This is the advantage of VST Transit. You have one owner of the project and the collaborators are working in different cubase folders and everything will be synced in one project.