Ask HN: Backing up only user-generated content?

I often am asked to do "software refurb" on old laptops prior to donating them to a worthy cause.

What tools are available to collect user-generated files for archival purposes? It would be awesome if such tools are aware of some of the most important files that wind up in obscure locations, like Outlook .PST files! Extracting a list of licensed software and associated license keys to return would be another part of this -- I guess some software configuration info would be useful to collect too.

Being able to run a tool overnight that could "auto-magically" compress anything important to a remote destination would be an awesome first pass at making sure nothing gets missed.

I have done full disk images to just grab everything, but the PartImage tool I used means I have to setup a VM with a virtually big-enough auto-expanding HD just to take a look (at which point, a tool highlighting user-generated content becomes incredibly useful once again!).

PS. WizTree does incredibly fast disk space usage reporting for Windows; I use it to manually track down and delete large non-user-generated files to avoid backing them up (and just to free up space). I'd appreciate any similarly fast (metadata-only) tools for other operating systems too.