I think the 350 in a low mileage decent unmolested example would still fetch a decent price one day, opposed to the 370 as it has not been to everybody's liking. A car in future years to come, depends purely to supply and demand with as said before an original low mileage example being top of the tree. The 240/260z became the sought after models, where as their later replacements ie 280zx 300zx have never had the same attraction.