Haggarty's makes a living understanding the automotive collectible market and they say the Z/28 is a future collectible. Their primary reasoning seems centered on the fact that it is a symbol of a new generation of high performance cars.
Think about it... this is a car that took things to totally new level... no sound deadening, DSSV suspension, LS7 (last of), barely street legal tires, A/C delete option, 440 more pounds of downforce at 160 MPH than an SS, CCBs, etc. and it ran head to head w/ a 911 GT3 and lost by 1 second. Add the fact that it didn't sell as well as GM had as well GM had hoped and it's lore will grow and grow. Just my 2 cents. It won't matter to me.. I daily drive mine (in the rain even), but for those who keep it to low miles, it'll likely be highly sought after down the road.
One last thing to consider.... it may not only be the last of the high performance NA V8s, but it may be one of the last high performing V8s altogether. Eco-boost V6s are going to be the future. Reference point...the new Ford GT.
http://www.thedetroitbureau.com/2015...-cars-of-2015/