One major difference between new and legacy reports is that with new reports, you can create one report/dashboard and run it within different scopes/contexts. With legacy reports, you had to build separate reports/dashboards for each context. Reports sources were tied to targets. In new reporting, target = scope. Can apply multiple scopes to a single report.
So it might turn out that you only need to rebuild a fraction of your legacy reports. You might try a transition approach like this:
- Review legacy reports starting at the Org level (target)
- Create the new report at the org level - remember all reports appear at the top-level Dashboards list, which is scoped for the Organization.
- Then run the report at other scopes and see if that meets your needs for targets in legacy report sources.