knowing the spanish empire and how bad they where in economics expect a crash of gold that surpases what mansa musa did in the middle east
1) This idea of the Spanish being "bad at the economy" is a 20th century retroprojection on 16th century economics and politics by economic liberals especially from the Anglo-Saxon world. No one could have predicted the inflation revolution that occurred as a result of massive amounts of silver back in the 16th century.
2) The reason why it seems the Spaniards were spending money left and right irresponsibly is because they were being attacked on almost all fronts by the French, the Ottomans, the English, the Dutch, the Germans and later on the Danish and Swedish as if that wasn't enough. These wars are what made Spain waste so much money and go bankrupt at different points in its history. Take them away and the financial spending of the Spaniards would have been used to teach economics at universities.
Now, the OP answered its own question. The thing with El Dorado is that it was the city of the Muiscas, which had many golden ornaments and idols. The idea of El Dorado being mythical comes more from wanting to find other similar cities - and the Spaniards would in Cibola and Machu Pichu and to a certain extent among the Pueblo in Nuevo Mexico - than from it not existing. Still, most gold and silver was taken from Zacatecas and Potosí, even if the Spaniards did strip a lot of temples from their riches, and a massive treasure fleet
has been found in the coast of Colombia.