I know locally in the US midwest the junk yards are buying scrap steel + iron for $200 US per US ton. Based on this, the 10,000 british ton ship at $200 / ton is worth $2.2 million USD to a dealer who will put a lot of labor into tearing it down. Torn down into just scrap, I would say the ship is worth about $8.8 million.
Good luck getting a carrier to the US midwest!
The correct answer is neither unless 1) the question is "which would save you more gas?" or 2) you plan to scrap one of your two cars instead of reselling them or trading them in.
Assuming both of your current cars work today, by reselling one you increase the supply of used cars which allows one additional carless person to able to purchase a car, and total gas consumption is now the sum of your two cars plus that of your new car. You can however impress your green friends by bragging about how you improved your mpg and "how much gas you're saving."
The billions being skimmed today (per a given quantity of trades) are less than the billions skimmed before.
Day traders produce exactly two things: personal wealth, and market instability. They add nothing to the GDP, and are basically leeches. Imagine if everyone quit their jobs and became day traders. Nobody would be producing any goods and the economy would collapse instantly. The leeches would have nothing on which to feed.
If by "market instability" you mean increased liquidity which increases 1) the amount of capital our society puts to work (we're more willing to invest in businesses when we're confident in the ability to liquidate the investment in the future at the time of our choosing) and 2) the ability of the market to efficiently allocate capital (lowers the transaction cost of moving capital from poor investments to good investments), I agree. Additionally some day traders increase the speed of price discovery penalizing speculators, which further increases the efficient allocation of capital (increasing production)within the market.
As a thought experiment - Imagine if we all became Doctors, nobody would be producing any goods and the economy would collapse instantly.
Wouldn't it be great if that responsibility was enforced so that the people responsible for the technology that sold stock on unconfirmed news lost a ton of money... oh wait...
A transistor protected by a fast-acting fuse will protect the fuse by blowing first.