In case you've considered putting it on your wish list, I believe a batch delete would be useful for Songs, Shows, or Midi presets. When working with a new band, I'll typically copy an entire database (thus copying some songs to be reused, as well as the settings and custom fields), then delete the shows, songs, and midi presents that I don't need for that project. It can be a chore, but still simpler than recreating my preferred settings and fields.