Only time will tell - here is what it has going for it:
Low production - 1,801 total produced including 440 in 2014, 1,288 in 2015 and 73 CTF cars (CTF = Captured test Fleet - cars for GM employees, marketing, press, auto shows, testing etc.).
Unique - Has 190 unique parts to the Gen 5 SS and has LS7 and Ceramic Brakes!
Look - it is a great looking car
Fun - it is a very fun car to drive for either track days or fun jaunts on your favorite windy road.
Success - 2 years of racing dominance until outlawed
Value - If you think the above are enough to make it collectible then at today's prices of $35k - $50k you won't find a more fun car to drive that can do serious track duty and be fun on the street.
So you there is no downside if you buy today, enjoy the car and you find it is collectible if you keep it.
Buying one to collect - well if you can get a low mile car - Silver or AGM (lowest production) and pay today's market for it , might be worth something some day - but won't be a good investment - so you better like looking at it - or better yet drive it and enjoy it!
Here is some Z/28 Information from when it was introduced - I will post detailed build information tonight when I get home.