Thing is, that aluminum industry in your example existed before the investment and independent from the investment. People need aluminum and are going to buy it.
If you have a signal to purchase more currency, and that currency's value only goes up if more people show up to buy it at a higher price, and those people can only get a payout if another tier of people show up and pay a higher price... See the shape of that structure? Vaguely... triangular?
Legitimate investment takes advantages of inefficiencies in pricing. It's not possible to always sell a commodity at the absolute ideal and correct price at the correct time, especially for an industry just getting its start. So people with a lot of assets can take some commodity, hold it for a period of time, then sell it wisely to take advantage of an existing industry. Or nurture it and reap the rewards when it is successful. See how cryptocurrency is potentially different? Most of the price of crypto is not supported by any industry. It's people buying more in hopes of getting rich quick. It's absolutely a bubble in its current incarnation, although hopefully it develops a more diverse underpinning as time goes on.
If it develops that foundation then it will be like investing in a fledgeling industry, nurturing it until it can become self-sustaining and profitable. If those applications don't come through, it's just another scheme.