Dropbox is working on something called Project Infinite, which should make working with large number of files a lot easier, even if you don't have the space for them on your hard drive.
Currently, Dropbox on desktop works by syncing all the files between your desktop and cloud storage, which can take up a lot of space on your hard drive. With Project Infinite, you can see all the files in your cloud account within the Dropbox folder on your PC or Mac, but the files won't actually be saved on your computer. These files will show up with a cloud icon next to them, whereas the synced files will show a green tick as they currently do. When you want to access the file, just double click on it, and the file will be downloaded and opened. This way, it will only take space on your hard drive when you want it.
This is similar to how things work within the mobile app, but with Project Infinite it is now coming to the desktop. This will work within the current Dropbox desktop client on Windows (10/8/7) as well as OS X.