For value and true unlimited storage, use a hosting company rather than Dropbox or alike. The problem with Dropbox and alike is they either limit storage and are expensive, or, offer 'unlimited' storage but restrict wha can be backed up - i.e. restricting you to a clone of your Mac/PC........which if your photo catalogue is on a NAS or equivalent is pretty useless. My catalogue is also 1.4TB and 32.000 images.
I use CloudHosted.com and pay £15 a month but there are cheaper plans with a longer commitment than month-to-month. That gets me unlimited storage via FTP.