Interesting debate.
Just to point out that if I called all the traffic immediately adjacent to CAS in the Luton scenario on a summer's Sunday afternoon I would never get the closing heading in!
I guess it depends on the environment you are operating but I tend to be very selective about passing ANY traffic information on traffic outside CAS to traffic inside. One example, when I do make the call, tends to be when traffic is operating east of Stevenage at 2,400ft ALt outside CAS and I vector traffic onto a base leg from the LOREL Gate descending to 3,000ft Alt and pointing straight at it. I feel it is nice (but not required!) to pass some traffic information on the observed traffic especially in these TCAS sensistive days!
Any EZY/BAL/MON/RYR jockies have an opinion on whether this is useful or should I save my breath?