There is a sheet rubber called mass loaded vinyl I used in my Accord- heavy.
It's just my opinion, but you're the first individual to talk sense (sorry, Others) I have to say. To quell noise you need:
i) 10-20% area-coverage of poorly-supported panels with constrained layer damping tile... no more than that! This simply kills resonances, oil-canning. It comprises a sandwich of butyl, aluminum, butyl and it is self adhesive;
ii) you need a contiguous "curtain" of custom-fit MLV, no gaps!; and you need
iii) a thin layer of CCF to "separate" the hung curtain of MLV from the car's structure.
Used to be a website and business called (I think) "sounddeadenershowdown" that was excellent with its how-to. Guy retired...
This is NOT easy to do!
Here is a site that has a web-archive of SDS... Takes a moment to load. Worth a read of the SDS site: https://expeditionportal.com/forum/...vehicle-the-right-way.225971/#js-post-2935500
OP... this is the first negative I've heard re the Boxsters/Cayman. Stands to reason the modern-day 911 is quieter. Yeah, you pay for it... but factory-engineered quiet is very hard to duplicate at home, so to speak.