I agree with the Cruft concept.. It's not just accumulated cruft, but accumulated modifications, settings, stuff you don't remember you did, etc.
Because of that, I think when practical, if you have the energy, it's healthy to start from scratch and force yourself to recreate your working environment on a new operating system, and move over your documents, etc.
This is a good opportunity for you to discover where all of your documents are stored, and start over with applications at their default settings, etc.
The one main caveat I will say with this approach is you have to preserve your old hard drive in some form (either leave the old physical hard drive alone and install the os on a new one, or a new computer, or fully image the old hard drive). That gives you plenty of time (months) to make sure you have moved all your documents over and not forgotten something.