I think that with respect to well rounded cars like ours, manual transmissions will always be more popular. Indeed Porsche sell three manual equipped cars for every Tiptronic that goes out the door--and that includes all of their tiptronic-only SUV's.
I think a better question with respect to the pro-touring formula would be:
How valuable is overdrive for a pro-touring car?
Whereas overdrive (either manual or auto) allows for transmission gear ratios that are far more appropriate for a well rounded car. Overdrive allows for a steeper 1st gear and better 2-3 gear ratios. Which combined with a middle of the road final gear ratio (3.50:1), works best with our relatively short rear tire diameters for excellent straight line acceleration. On the other end of the equation, an overdriven high gear provides better fuel economy and higher top speed. Performance nirvana.
I always found my TH350 / 3.90 / 275/40ZR17 combination to be somewhat dissappointing. In fact, I'm bummed that PHR selected a TH350 for G/28. I understand that cost is an issue, but a built 200-4R or bone stock junkyard 4L80E would have better fit the performance goals without breaking the bank. We can argue price all day long, but balance price with performace goals and I know I'm right. (I didn't get very far arguing the point with Johnny, though)
So Bringemout
If a TH400 is in your future, I recommend backing it up with a Ford 9" so that you can try different final drive ratios until you're happy. When in doubt, a 3.42 or even 3.31 will maximize all around performance at the expense of E.T.
Even then, when the road gets curvy, or if you find some room for high speed testing,
you may find that the 3 speed trans is holding you back.