As I recall history, Santa Anna fought the American-Mexican war during the 1840s to gain an undisputed border with the United States. Today, Mexico does not have any border disputes with any of its neighbors. They have all been settled by treaties.
While the four Knox class have ASROC launchers and ASW torpedo tubes, there are no missiles or torpedoes to use them. Mexico bought these leftovers for $7 million each, sufficient as ocean going gunboats. Besides the two Bronsteins based at Manzanino as training ships, the rest of their fleet is mostly OPVs and patrol boats required to defend their fisheries and provide search and rescue capabilities.
Recently two Newport LSTs were acquired to replace older WWII LSTs. This year Mexico acquired two Austin LPDs to provide housing and sealift for their army, Mexico's answer to the aftermath of Hurricane Rita. More of a civil defence purchase than a naval purchase.
Its a coast guard type of navy, not a warfighting one. With no enemies or border disputes, Mexico refuses to intervene anywhere, even in the Caribbean. Frankly, with all of the uprisings and civil strife, Mexico's armed forces have their hands full keeping their country together than to partake in foreign entanglements or shows of force.
Considering that over ten percent of their population has left Mexico to immigrate to the United States, along with its high unemployment rate and its poverty, in my opinion Mexico is doing well building nice new OPVs.
Of course, I have a different opinion about its government's handling of its economy. With the resources Mexico has, there shouldn't be any poverty in Mexico.