Just happened to see that the configurator is up on Porsche's US site.
https://www.porsche.com/usa/models/7...ts-4-0-models/
Maybe I did not look or click carefully, but when configured similarly, I was disappointed to see the price difference was only about 4-5k.
Sure, the power top is great and 5k is no small amount. But you do miss out on a much nicer front end, GT-tuned suspension, more power, higher redline, and a bunch of other bits. Also, the Spyder is bound to hold up better on resale.
Perhaps this just means that they priced it right.
A good GTS 4.0 review that references the Spyder: