Some of those high prices seem like the result of speculation, or people pouring their money into 'something physical' the same way that market volatility sometimes ends up with a rise in gold prices.
How can a diamond be "used"? I think it's only the person offering to buy it trying to convince you of this.
Diamonds are cheap and easy to appraise, and with laser etching easy to identify. I buy all my ice with AGL certs off eBay.
There are more degrees of freedom than with something like gold coins, so diamonds aren't fungible. It adds complexity but I don't think it hurts resale that badly.
If the resale market were so much cheaper, that's where everyone would buy their stones, right?
