Not only valid for vintage aircraft, but right now, there are lots of airplanes sold WAY under value. With the current economic depression, those who have the money to invest in one of these may well find themselves with a nice profit one day, once the prices will go up again. And they will.
To be considered of course is the cost of upkeep, maintenance, hangar e.t.c. for the time.
I was looking around for more than 5 years to buy something nice to fly with but I am glad I waited. It's a buyer's market now if it's ever been.
Best regards
AN2 driver