Do you see value in rare baseball cards selling for millions of dollars? That's the same, but the card's authenticity can be verified cryptographically rather than through complex means like radionuclide analysis and such.

Yes. A rare baseball card (physical one) might be worth some non zero money to many people. But only as long as it is physical card. Any digital asset that represents it would be valuable to if it is NFT. This is nearly same as holding some bits of data in your bank account. Those numbers are valuable because they map to real world currency which the bank is holding for me.

Physical goods would still need the same authentication if they were tied to an NFT, and may be rare as a consequence of their nature.

What's the value of pretending an easily duplicated digital thing is rare?

I realize that an NFT minted on a given chain is unique, but so what, that doesn't make it unique and interesting they way a baseball card might be.

Unfortunately, it is impossible to cryptographically sign a physical object (like what, enumerating all of it's atoms and their positions?). NFT is only valuable if the creator promises she will never sign any more identical objects in the future. And she is incentivized to do so by way of receiving royalties on all future resales.