Agreed about it making no odds other than keeping crap out of the engine, the additonal pipework may affect flow from a power/economy point of view but doubt it is measurable.
Just don't go doing this on a modern vehicle, many ecu's 'know' it has been blocked or has failed, this throws a code along with the MIL, and recently a MIL light staying on will fail a Spanish ITV, unsure how UK MOT stations are dealing with this?
Also the machinery in test stations is being programmed with expected values, this allows he inspector to get an indication if something is amiss, interesting this facility is only being implemented on petrol engines?
Regards
Dave