I'm in the old car, street rod, community. We are seeing a dramatic drop in values, well before the virus hit.
The consignment dealers have their whses loaded to the gills.
As the "car guy" age groups get older, they change their preferences. Many followers of various cars, are not seeing "new guys" with those same interests. The cars for sale, are sitting for considerable time. Once a prospective buyer steps up, it's usually w/ a "low ball" offer.
A case in point: A friend's 55 Chevy is a $100K+ build. It sold at Streetside, for less than 1/2 of it's initial cost.
Once the "out at any cost" syndrome hits a hobby, the bottom falls out.
The old saying, "buy one already done, is a lot cheaper than building it", is truer than ever, in today's car scene.
As for the Buicks, I see it being no different.