I follow the collector market a bit. Celebrity cars typically hold no additonal value beyond the timeframe that the celebrity is newsworthy- and then only to a very narrow group- typically fans of celebrity, not automobiles.
The cars that have been owned by celebrities that have achieved elevated-market-price collectibility typically are cars that were unique or special in their own right.
Cars owned by some of the biggest-name sports and entertainment celebrities seem to hit the market all the time. But they usually don't yield any premioum prices- at least not sustainable prices dureble through the vehicle changing hands.