Not true actually. There are far more warbirds in flying condition now than at any time in history.
You guys are misunderstanding Vraciu and nitpicking semantics.
There are more flyable warbirds (mostly fighters) than since about the 1980s. Unlimited and lower class racing has inspired people to restore fighters that were nothing but balled up metal into flyable machines. Sure, they aren't "stock" but often end up being sold and are restored to factory condition and often in the colors it used during the war........or wearing famous plane colors.
Many of the planes restored for racing would never have been restored if not for racing.
That said, if you like vintage sports cars and want to restore one, I've found that vintage race cars that have sat for many years are often the best place to start for a restoration since the pool of original cars has shrunk so much as of late.