I'm not sure this is true. A car buddy of mine believes the ES has a different suspension and transmission than the Camry. However, let's assume these are the same. Does that make them the same car? No. You did get better build quality and paint and different performance characteristics and that is what I paid extra for. With rebranded detailing products you may have the exact same item and different packaging. My point is that the two examples are very different.
As for the Cayman, I believe it has a different engine (definitely different tuning) and suspension. In that case as well, an extra $10K goes a long way. I have read several reviews on this car and most feel it handles not only better than the Boxster but the 911 as well.
Your acceleration numbers are a bit off. My car has been timed at 7.0 seconds and several of the auto mags also got the same numbers.
The reason I am making a strong case here is that you are implying the Camry is essentially the same car which I know to be false. I have had two ESs and a Toyota Camry which my wife drives. Several neighbors have the new Camry and I know that car well too. They are very different automobiles. The quality of manufacture is different and the performance is different. The Camry does not corner as well nor is the paint as high a quality. Interior noise is higher on the Camry. Dealership experience is far below that of Lexus. I take both cars in for service and it's night and day in customer service...
It's not like Lexus slapped on a badge and raised the price. They are built on different assembly lines to different standards for different markets & users.
I can understand if people don't want to pay extra $ for the more luxurious car but don't tell me they are the same when I know they are not.