Yup, that's my answer too... I had windstops on both Z3 and Boxster (came with the cars), but used to ride in those a lot more...
I think you have hit the nail on the head...It is a thing...
The diffuser is quickly and easily removable..
Why buy a Morgan if your going to start putting appendages on it to stop a bit of wind, for me the fun is that open drafty feel on a crisp day in a flying jacket. Why not get your other half a lovely flying jacket with a big collar and a suitable hat.
Adrian
Buggered Off, to a modern none leaky car, heart's still ticking
used to ride in those a lot more... 
