Shameless plug for my product, ExpanDrive

http://www.expandrive.com/expandrive

Mount Dropbox as a network drive. Smart local cache. Access the data on demand without syncing the repo in first. Also supports gdrive, s3, sftp, onedrive, box and more.

Makes a 1TB account make a lot more sense if you only have a 128GB SSD. Use selective sync with the primary client to only sync a portion of your Dropbox. Then use ExpanDrive to offload the rest and access it as needed.