Are proxy fields really necessary, or even that useful?

I, too, find little use for them, and routinely take steps exactly like the ones you describe. About the only circumstance I can imagine that might be useful would be when: (a) users will want to refer to a record by some field they know well, such as an ID from another system or an email address, and (b) that field is unique, but (c) you as the admin have other reasons for wanting to use Record ID# as the key field. As a related point, I think a proxy that's not unique may be an invitation to user-confusion.