So far I've bought a reasonable super car for twice; comet and vacca. Like everyone's habit, as soon as it being delivered, I brought that expensive toy to LSC and wanted to see the selling price, which ended up realizing that this car can't be sold back due to more than 50k worth of dollars.
Because of this, now I no longer see the point of buying super car, modify it, and when I'm bored with it, I couldn't even get a quarter of the total money spent on that vehicle back. This is like an obvious trick of R* to lead players to buy their Cash Card craps.
They're like saying "wazzup amigo, here are super cool cars, but they're expensive yet you have 2 ways: work hard or buy cash cards. Oh wait, don't forget you can modify that too and it cost money, so you can either work hard again or buy cash cards. What? You spent too much on that and now you want to sell that super car which worth 50k+? No man, c'mon we have cash cards for you to buy, but you can also choose to work very hard again and throw that old super car of yours like a trash.