I'd start with exporting and archiving any report that hasn't been viewed in the last 3-6 months that isn't being automatically sent. But after that cleanup -
Build a Report Report (yes, really), with the following columns:
- Name
- View
- displayname=View
textmode=true
valuefield=view:definition
valueformat=HTML
- Filter
- displayname=Filter
textmode=true
valuefield=filter:definition
valueformat=HTML
- Grouping
- displayname=Grouping
textmode=true
valuefield=groupBy:definition
valueformat=HTML
- View Link
- displayname=View Link
textmode=true
valueexpression=CONCAT("https://<your domain>.my.workfront.com/lists/views/view/",{viewID})
valueformat=HTML
- Dashboards
- Views this Month
- Entered by Name
- Last Sent Date
What that will give you is UGLY but the best way I've come up with to audit anywhere a field is being used that I might need to update. Then you can use the filter on the report to look for anything with the fields you want to update in it, plus the dashboard/views portion allows you to prioritize which reports are more crucial to update first.
If it hasn't been looked at for more than 6 months, isn't on a dashboard, and doesn't have a last scheduled send date, update it to 'PENDING DELETION XX/XX/XXXX' in front of the report name to see who objects.