An ordinary violin may cost about 1000 dollars. A Stradivari may cost some millions. Why are Stradivaris so expensive? Are they worth their price?
Some violins from that era are so expensive for the same reason that some paintings from that era are so expensive: that's what the market will pay.
There was "blindfold test" some time ago where world class violinists compared their own Stradivari with the best modern instruments. They couldn't reliably tell the difference.
There's also probably a lot of psychology involved. If you were to give a violinist two Stradivari to test and tell them one was a copy, they would almost certainly sound much better on the "original" than on the "copy".
A Stradivarius is worth what the buyer paid, at least to the buyer. I went to a concert some years ago (in the 1950s) and the violin soloist played several violins and asked the audience to guess which one was which (A Stradivarius, A Guarnerius, a good modern violin, and a cheap modern violin.) I couldn't tell. My mom identified them quickly and correctly. So did the music faculty of the local collage. I don't know whether these violins wer worth their costs (which I also didn't know), but I do know that there are people who can tell the difference.
A 1000$ violin would not be considered as acceptable by an ambitious amateur, let alone by any professional musician. But a five digit price tag will only reduce the factor.
I actually don't see a difference from violins to goods of any other market: beyond a certain "saturation" limit, additional money will provide smaller and smaller benefits.
The answer to my question is to find in the videos from which my question arose:
In 2011, a Stradivarius violin in pristine condition sold for $15.9 million. And then, in 2014, another Strad went up for auction with a minimum bid of $45 million. That auction failed, but it underscored a trend: The price and prestige of Stradivarius violins keep climbing, driven by the insatiable demand of investors and professional musicians.
and there are much more videos giving information and trying to answer this question.
(also the point with the blind test is mentioned in the first link above.)
Here are a lot of other question you can ask about Stradivari Violins:
Search for: Do Stradivarius really sound better?
How many Stradivarius violins exist today?
How much is the Messiah Stradivarius worth?
What makes a Stradivarius so special?
How much is a real Stradivarius violin worth?
Who owns a Stradivarius?
Do old violins sound better?
I know this is not an answer to my question.
Btw.: For the violin I've bought on the flee market in Amsterdam for my son 40 years ago I've paye about 80 dollars (about 100 Swiss Franks) and its value must have been ten times as much. But it was not a Strad ...