The Spanish had grown up knowing that gold could be swapped into land and wine and women. Get a lot of it, go home, live the good life. I doubt it was more sophisticated than that. The evidence suggests that the Spanish didn't have an academic understanding of currency, because the influex of silver caused huge inflation in Spain and damaged their economy.
> it's univerally a good currency
It's not. Metals don't function as currency even in the world we live in. You can't go into a shop and buy a computer with a piece of gold - nobody is set up for it. It functions less as a currency even than something like bitcoin, which you can occasionally find something quoted in. With gold - you won't find someone quoting food, land, or shares with it, or set up to accept it as payment.
There's a concept called 'store of value'. Gold is regarded by many to function as a strong store of value. In fact, recently it hasn't - it's gone up significantly for several years and then down this year.
But that's a different thing to currency. And it's not unique to metals - land and cocaine tend to have those properties also.
> It may be that the Inca never used gold as
> currency, but it would be hard to substantiate
> that claim, I would think
You've set down a default assumption that is incorrect - that gold is a universal currency. Then you've followed on to say that - therefore - it should be assumed that the Incas used gold as a currency. This is invalid.
The article says there's an absence of evidence of markets from the Incas, and painted a picture of how life worked. If you think that gold was valued as a currency, show some evidence.