This argument could be applied to literally every depletable resource in existence. If utilized efficiently with reprocessing and breeder reactors the world's proven Thorium + Uranium reserves would last thousands of years, even powering 80-90% of world energy use. By that point we should be using either fusion energy or beamed power from panels in solar orbit, depending on how optimistic you are - and if uranium does turn out to have a miraculous alternative use we'll have a sufficiently developed space program to mine it from somewhere other than Earth.
I disagree with the notion that we'd be producing 'relatively unimportant amounts of energy' when we're talking about the only geography-independent near-zero-carbon energy source with the proven capability to provide base load power for an advanced economy, unless you think anthropogenic climate disruption is no big deal.
There are no other resources depletable in the same sense - even if you burn coal or oil, equivalent resources can be synthesized. The rest is usualy not depleted in the literal sense, only put into use and may need to be recycled to be used elsewhere. But the elements used in nuclear fuel are completely destroyed in the process and there may be no easy way to recreate them.
Uranium and Thorium could be produced by nuclear transmutation in the event we discover some miraculous property they have ten thousand years from now. This is non-trivial, but it's essentially the process used to produce plutonium for nuclear weapons and we managed to get pretty good at that.
I disagree with the notion that we'd be producing 'relatively unimportant amounts of energy' when we're talking about the only geography-independent near-zero-carbon energy source with the proven capability to provide base load power for an advanced economy, unless you think anthropogenic climate disruption is no big deal.