Vichtz

When you say age well, what does that mean? If you're talking about looks the 370z will "age" better simply because they are too expensive for teenagers to get but cheap enough for a middle class person too get. By that time however you're expected to be having a family and ****, so the 2 seater 70 doesn't appeal to most. So that is why you see less 70's, and therefore it will hold it's value more due to rarity.
HOWEVER, as for popularity and standing the test of time, the 350 has it hands down. Maintenance on a 50 is cake (****, even changing the oil on a 70 takes forever...).The aftermarket is 10x more expansive and affordable allowing for every taste, either classy or ricey, to be realized. It is also very affordable for teens who have no real parental/transportation responsibility so can manage the 2 seater life. Also, the 350 made a much larger impact on the "car scene" from the get go because of its stark tear from the 300 styling. Go to any car show or race event and there will be more 50's than 70's. Just from a social perspective it is apparent that the 50 will be around longer. How many times have you gotten the "nice 350z" from some random wannabe boy racer punk? The 50 hit hard and became the sensation because it came out when the "scene" shifted from old dudes and muscle and became about younger generations and the "underground" and "F&F racing" all that ****. So will the 70 be more valuable later on because of its rarity and looks? ("nice porsche"...) YES. But on the other hand the 50 will be around longer and will it be more popular? YES.
So it comes down to whether you want ease of maintenance, more popularity, and complete customization with less money per mod. Or if you want to have that slightly higher end look without the higher end pay, but less customization per dollar, more maintenance, and less popularity.
"age well" is relative... Damn that was long winded...

__________________