[Perfectlap]

GM are eager to take on Porsche, they've already identified Porsche as their biggest target. With a head-spinning number of Porsches for each model on offer, GM know they will have to cater to every type of buyer. You want a Stingray roadster with the biggest engine. Fine, what color do you want? You want a stick to stir? No problem we won't shoehorn you into automatics only (aka PDK).

p.s.
If an old school suspension and old school engine is/will be beating the pants off $200K Porsches at the N-ring, where you MUST have scalpel-like execution, over a very long distance, to be the fastest well then what does that say?
Also, I'm not so sure about your contention that the Corvette will not be fuel efficient for a car that is substantially faster than an over-priced (imo) Porsche roadster. I guess you can justify the Porsche tax on subjective grounds then its not over-priced. But spec'ing performance upgrades (in league with Stingray upgrades) to any Porsche no longer puts you into $50-$60K range. In fact, pretty un-performing upgrades to 981 S will put you into a price range that borders on drunken sailor spending.

Now to be clear, I'm not saying I would prefer a Stingray convertible to a 981S (I'd go tin top on the Chevy, not convertible too big to feel like a roadster). I'm merely debating the point of "what are you really getting for that Porsche tax".
I think folks have been blindly justifying a premium that isn't making the cars any quicker and they're not keeping Lexus up at night on reliability. Over-paying just because? Perhaps the type of buyer that Porsche is shifting towards aren't the type to really analyze value, they merely want the perception of exclusivity -- that really doesn't exist anymore, not with hundreds of thousands of Pcars for each model series rolling about. It's like a Rolex, they make over a million of them a year, the high price isn't even justifiable on the grounds of exclusivity anymore. $800 of actual watch, $4,200 of image.