and you'll find the car is now worth about half what you paid for it.
Depends on the car, but for most cars they are worth far more than half, despite the truism. The higher priced the car, the less they lose as a percentage.
But yeah if you pay $30,000 and LITERALLY drive it across the street, there is no way the dealer is going to pay you more than the wholesale cost on the vehicle new.
Think about it... why would he pay you more for your slightly used car than he could pay for a brand new car?
But given the vehicle literally has under 5 miles on it, and you can show a bill of sale proving you've had it for all of 10 minutes, he will easily pay you a few k less than his wholesale cost, then list it for just slightly less than the car would cost new. (which of course is several thousand more than he gave you for it... because that's how business works.)
If you want to get value for your used vehicle, sell it privately. Any dealer who buys your used car needs to buy it from you at a price where he makes decent enough money selling it that its worth showing up in the morning, after his rent, utilities, insurance and other expenses are covered. Not to mention any expenses on the vehicle itself, from detailing it to doing the brakes that you didn't mention were way past overdue... or whatever.
The point is, buy a new car, drive it off the lot, and sell it privately and you'll be asking just slightly under what you paid for it. And you'll get it.
Look at any car lot... are the 1 year old 2015 cars with 7-10k miles on them half the price of a brand new 2016 one? Nope. Not even close. Cars, outside of a few collectors items, are depreciating assets but they're not nearly as bad as you seem to think.