Couple of comments:
Porsche owners (I currently own a 981 Cayman S) share the love for 2 seat, nimble, pure sports cars with a definite GT feel. My Cayman gives me the exact same feeling I had driving my new '77 280Z back in the day.
As far as value for that '77 280Z, @riverstonefly2 years ago I paid $18,000 for my 90,000 mile, extremely original, rustfree "78 280Z (no sunroof, impeccable interior) that was only missing the original radio and wheels. Depending on the mechanicals, and the actual quality of the body panels and chassis, I think that candidate is very strong and although a price of 10K would be fantastic, I don't think it's very realistic. I think a fair price would be between 16 and 20K in the current market. That would still make it a good deal since your expenses to bring it to excellent shape would be very reasonable due to the overall condition.
The bonus is that despite the opinions of all the 240Z owners on the forum (no nasty comments please ), the 280Z will provide you with a much more refined drive, similar to your SC !