I¡¯ve started deleting photos from a couple of months ago which were
inserted images (oh how I wish I could select several at a time and bulk
delete... lol).
Other than cluttering up the Emailed Photos album, is there a reason to bother deleting them?
An alternative is in the Message Formatting section of your group's settings: Delete Old Attachments when out of space, and then just let the site deal with them:
For what it is worth, some ideas to make it easier to delete or consolidate these repeat photos have been discussed in beta.