As a past 392 w/ A8 owner, I agree with most of your post. The A8 does provide seamless, uninterrupted acceleration. It also launches harder/ easier than the M6. It has lightning fast shifts. It is a great automatic transmission.
That said, I personally don't find your "involvement" statement to be accurate. Honestly, I feel the total opposite. I am actually a bit surprised that you would say that, coming from a manual transmission in your past Porsche and GTO.
I am sure you have driven your cars outside of traffic, and on other than just straight roads. Its on a twisty road that I find the manual cars allure to be its strongest. (althou, they are still quit fun ripping thru gears on the straights)
I have no experience with the Porsche, but I have driven the 6 spd GTO. It was a far better car than what most people think and the manual transmission gave it a "special" feel/involvement/connection/engagement. I wouldn't want that car any other way.
To claim the only "involvement" with a manual trans is deciding when to shift, is a huge understatement. It presumes, other than that decision, they are the same.
They are not the same. They offer totally different driving experiences. To say they are otherwise the same, is a discredit to them both.
Whether you prefer one experience over the other, is a personal choice. (There is no wrong choice.)
For myself, Its not ALL about the usual performance matrix/numbers.... 60 ft times, 0-60 mph, 1/4 mile ET, top speed... they are important to me, but they are not the be all/end all.
I can't find the words to describe (accurately) why a manual car drives differently from an automatic car, they just do.
Maybe its more about balance, control and yes, "involvement."
More about how a manual car makes you "feel" when you drive it.
Definitely more about smiles, than numbers.
Its also more than just the shift lever, the third pedal plays a huge part in the equation as well.
I'm glad that the Challenger, Mustang and Camaro's have a manual options. Disappointed to hear that the new C8 Corvette will be with out it. There are not many manual options left. They all will be gone soon.
There are less and less people that even know how to drive a manual. They too, will be gone soon. Sad on both counts.
To answer the question of the original thread, "age or preference?"... I think it is a combination of the two.
But hey, this is just one 52 year old "Gear Jammer's" perspective.