lhammy. Your two items of risk concerning Mexico are not valid IMHO.

viz: Or Mexico could nationalizing mines, or impose huge tariffs.  No, it's not reasonable to expect that a huge jump in silver prices will go unnoticed and that they will simply allow their metal to walk across the border. Or Mexico could monetize gold and silver, probably making it's export illegal altogether.

Mexico is part of the North American Free Trade Area (NAFTA), which is an agreement sealed in blood with the transfer of hundreds of thousands (even millions) of jobs from Canada and the USA to Mexico.
The two items you mention would require Mexico to tear up the NAFTA agreement, which would threaten repatriation of all of the manufacturing that has relocated there. The jobs of millions of Mexicans would be at risk at a stroke.
And for what end? The Mexican govenment now gets more from NAFTA manufacturing and open access to Canada and the USA for its agricultural sector than it would ever get from nationalising precious metals.