Just to chime in - I have a 2013 Boxster S along with my 96 NSX. The last week, I had the NSX out getting a timing belt / WP job done, so I had a good solid week of driving the boxster S.
By the numbers, the boxster S would eat my NSX alive in every measurable category. It feels torquier and more linear from down low, and grippier too. It's nimble as all hell and *sticks*. Steering feedback is great as is brake pedal feel. The flat 6 sounds better stock with PSE than my c30a does with the headers and exhaust. It's a fantastic car. Had I never driven the NSX I probably would pick it as "top driver's car" of all the cars I've owned and driven with the exception of the lotus elise (which has its own share of problems and compromises to get that title).
But, I still notice all the things my 21-year old NSX does so well, sometimes better, than the boxster S. When I yank the wheel - the NSX goes. In the boxster S, it's still lightyears ahead in response time compared to even other high end sports cars - but there's still a "squish" in the body and suspension before it plants and goes. The NSX just flows with zero lag time between input and response.
The biggest difference to me though, is the ergonomics. The boxster S is such a small car - yet it felt like I was driving a bathtub. High sills and large feeling compared to the snug, jet-fighter cocoon of the NSX. Visibility kicks the boxster's coffin feeling to the curb easily. the 981S scrapes everywhere - while the NSX does not despite the roofline and beltline being an inch lower (and the 981S is on the lowered sport suspension with 20" carrera wheels as well).
In most quantifiable ways, yes the 981S is a better car on paper. I'll take the NSX any day, though. It's the intangibles that the NSX excels in, and you can't buy/build that stuff easily by throwing faster, bigger, better parts on it. The NSX is greater than the sum of its parts.