In the US can't you get a base Vette for that price and year/mileage? If so it beats the rest of the cars you mentioned 
You can possibly get a base vette for that, but the insurance would eat a young up, besides, the base Vette tends to attract the "goldchain" wearing set. Once into the Z06, ZR1, where people with money tend be. But Porsche people and Vette people are different. Vette people like the bang for the buck, and don't mind a sucky interior that smells like glue (Z06 on a hot day).Porsche people like the German feel and quality interior, and the fact that the engine is in the wrong place. And are expensive to fix.
One if lucky could find a 3 yr old Z06 for 31k, but that might be rare because the people want to keep them, and I would inquire about the previous owner dogging that car out on the track. I knew a guy with the C5 Z06, and he was always at VIR.
But, the cars listed have almost equal pace, they run the gammant of AWD to RWD and luxury and track, also quality. One also has to think about perception and usability. The 370Z and the Corvette are 2 seaters.
ND, when I was in college I had a opportunity to get a 911 SC targa, someone was "curbstoning" it, and I realized that the car would have needed about 20-30k worth of work to it. I estimated that by using Excellence Magazine's guide to 911s.
