How much do we spend in the US each year on military to ward off some supposed future threat to our existence? Is it deemed “economical” to do so? I think nuclear should be viewed in the same light given the threat we know that it solves for.
You don't spend it for some future threat but to ensure safety of world oceans and to allow globalization and free trade (which benefits US the most). Without that power projection US wouldn't be the only tech/economic/military superpower.
If the US can make it so oil is worthless, that would be a truly useful strategic endeavor from a geopolitics perspective. How many terrible regimes survive because they have money from oil? An abundance of energy should be a great stabilizing force on the world.