Hi Phil, I don't really have much to offer here as I've never driven an auto, but let me just share a couple of quick thoughts on my experience. As an ex-NSX owner (albeit with the car still sitting in my garage) hopefully I'm reasonably unbiased.
I went from an S2000 to a facelift MT. I had both cars at the same time for about 4 months before I off-loaded the S2000, so could make some comparisons. Sure there were some similarities, but in brute performance terms, the NSX was soooo much faster and more dynamic than the S2000. FWIW, I actually preferred the gear change and steering on the S2000, but in every other respect, the NSX trounced it. The S2000 had a claimed 0-60 of sub 6 secs. Of course I never did a drag race, but I really wouldn't be surprised if my NSX was sub 5 secs. Take this with a pinch of salt though.
I had the clutch replaced on my NSX a year or so ago (with only 22k on the clock - shocking). This TOTALLY transformed the car. Beforehand, the CL was pretty stiff and heavy, but afterwards was so light and sweet. A well set-up MT is a real joy.
My daily driver has a DCT, which I just love for day-to-day driving. But for a car to enjoy over the weekends, for me, it HAS to be an MT. I'm convinced that one of the reasons why two years' worth of GT4s all sold out within 3 days of taking orders was because Porsche only offer an MT on them. Everyone's different, but if I were in your shoes, I would DEFINITELY hold off for an MT. NOTHING can replace the sheer pleasure of sweet manual gear changes eating up a winding country road. NOTHING. And for me, this was what NSX ownership was all about... as well as the sound of that V6, the forward view from the cockpit and the sheer 'place-ability' of the car.
HTH. And all IMHO of course.
Mani.
2003-2011: S2000
2011-2015: LBBP Coupe
Present: 911 50th Anniversary Edition