My question was not if but how much value it would add.
So, Danny, you're asking "the glass is half full" question... I get it!
But the basic value of a Z28 has little to do with appearance options. A Z is all about performance. So, document the top was an original option, keep all your receipts, add the cost/labor of putting on the vinyl top (and any other work you have done) to what you have in the car, figure what appreciation you would like to have out of it; and then, declare to anyone who is interested that is the "value" of the car.
...And then, be prepared for all "the glass is half empty" responses.