If every single inch of a barren rock moon was used for, say, doing yoga, and you wanted to start a new yoga zone, you couldn't do so unless you were able to secure some of that (scarce) square footage. And the previous owner would set a price given this fact.

Yes, you need to *do something* with it, but the fact that the square feet of the moon are limited is what makes those square feet valuable for use.

Same thought experiment on an infinite rock moon would make those same square feet _themselves_ worthless.

You can't divorce "opportunity" from the land's existence, but you can nullify it if the land is infinite (or if people want to do nothing/not exist). As long as it's not infinite and people want to do anything (including just exist in time and space), the "opportunity" bit you mention is always present and therefore intrinsic to its scarcity.