I wouldn't trade my M3W for any M4W.
Yes, I think that if I had been in the position of not owning a Morgan when the M3W came out, I would have bought one and been very happy with it indeed.
But I've owned my 4/4 for 16 years now and there's no way I'm getting rid of it, so an M3W would be an addition rather than a replacement. In terms of miles covered, the majority of my Morganeering is either commuting to work or going on holiday, neither of which I can see me preferring to use a 3 wheeler for, especially not in wet weather.
But for summer weekend blasts around the back roads, I can see they offer an experience you simply wouldn't get with anything else. I still hanker after one, but it's a lot of money to spend on something I would probably use for less than 500 miles a year.