If I have read your posts correctly, you sold your E89 with the intention of getting a 'vette.
So get the 'vette.
If it's a weekend car running costs, parts, etc don't really matter. Why would you buy a 'fun' car that does 4mpg more than another 'fun' car if it's not the one you really want?
If you get the Porker because it's the more sensible option (still not exactly sensible), once the honeymoon period has waned, you may still want a 'vette.
The Cayman is a compromise of your wishlist....you said you want a V8, convertible, something different, muscle car. The Porsche is none of these, the 'vette is all of them.
I voted Cayman but I ain't buying either of them so our preferences don't matter.
Just get something soon and make sure you show us pictures.

All good things come to those who wait. I'm really impatient which explains a lot.
2024 Audi A4 avant 40 black edition petrol
2025 Ford Focus ST 'track pack'. Go-kart with sat nav.
Z3 'free litre'. Project and a half.
No Z4 anymore!