I can only see "value" for NFTs in context of some digital application which can constrain supply of the thing the NFT represents. e.g A chat application might

I can only see "value" for NFTs in context of some digital application which can constrain supply of the thing the NFT represents. e.g A chat application might decide that only the owner of the nyan cat NFT can use the nyan cat emoji. So if there's a different blockchain with another nyan cat, it doesn't really matter, as long as the chat application doesn't use that other blockchain.