I suspect resale value will only hold true as long as demand exceeds supply and people can't get their hands on a C8. This could last into 2022 with the decreased production time for the 2021's. Maybe I'm overly biased (yes; I'll admit that) but I expect once more C8's hit the streets and people have more opportunity to see them "up close" and talk to friends who have them, that will increase demand even more for the 2020's and next year models as long as GM keeps the price point low and continues to tweak any defects or offers better options. This also will depend upon COVID and if it continues to plague production by shutting down Bowling Green (heaven forbid!). That could again reduce supply and increase demand. So there are still some unknowns.
But if things settle down and enough "new car" buyers have their C8's, we're then into the "more practical crowd who don't need the new shiny penny" aka "those who wait for used vehicles and for prices to come down". For those buyers, they will look more at what's available or will soon be available for sale, and they may very well pass on a 2020 to get (for example) a 2021 with a non-Z51 package with magnetic ride...or the 2 new colours for 2021...or (who knows?).
Plus with things settled down, the "new car buyers" will be attracted to that "new factory smell" and they'll have access to the latest and greatest options at the time and they'll want to custom make their cars with those options and they'll be willing to pay for that privilege instead of buying used. So they won't go looking for a used C8.
So if you're thinking a 2020 C8 will be a "collector's item" I don't see that in the long term. If they produce the hoped-for 20,000 there will be too many of them to ever be considered a rare collector car. If you're looking to maximize your resale price, it's likely best to sell within the next year or so. Recognize as well that the Z06 (and later) versions will up the game and capture the market's attention by being the "talk of the town" and take up all the reviewer's ink and videos and comparisons with other vehicles such as the Porsche 911, so all of that will point the spotlight away from the "yawn...only a basic C8 Stingray"...
For anyone who's put a deposit down and will get a Z06 and is already driving or will soon drive a C8, the timing could be perfect for selling the Stingray to get cash for the Z06 C8, depending upon when the Z06 version comes out. Hopefully that will work out for them.
Just my 2 cents and as always, only time will tell.
