If you would like one, go for it. I think that the badges are more popular on the 100k audaxes, and AAA events, than they are on the longer rides. Each year I have a couple of people wanting a badge on completing the Upper Thames 200. The badges are not expensive. Sometimes the organiser will have some badges available on the day. Others (and I'm afraid this includes me) take the orders, and send the badges with the validated cards. Be careful to distinguish between "badge" and "medal". I have had requests for badges where I subsequently discovered the requirement was actually for a medal.
I keep thinking I ought to stitch my RRTY badge(s) to my Carradice, but I'm loathe to add stitching holes. Could glue it on, I suppose.