Do owned cars show up during wheel spins?
Yes and you will eventually get duplicates. Horns however seem to have disappeared from them now that I have them all.
Yes, you can get same cars from wheelspin. It’s ridiculous imo. It must convert to its price and give that money would better i think.
I think that the main reason that they give duplicates (and not instant cash) is because of the fact that perk trees exist for the individual car and those include rewards that arent specific to the car.
Darn, that rules out my brilliant plan of buying all of the cheaper cars immediately. 
To me i have most common cars before i get first duplicate common cars, and for rares i also have most of them before getting first duplicate. Im pretty sure that wheelspins are coded that way that you have mutch bigger change to get car that you dont own yet. But offcourse it’s works only each rarity differently that you dont have any better change to get legendary even when you own all other cars. i have myself do that lately that i buy allways cheepest car that i miss and now all cars that i dont own cost over 1m but when i last time got legendary car it was cheap audi.