something closer to Earth where the return on investment is clearer and sooner.
What exactly? The best places on the moon are already controlled by the Russians and Americans.
Yes, North Korea hasn't been relevant, which is why they would be the ones to try and do something like a long shot Mars mission to gain that relevancy on the global stage.
Them trying something is likely, they still try today. The problem is that they can get to Mars. Honestly, them being able to go to the moon would be a huge achievement, especially alone. Now them going to Mars without help from the USSR and China is basically ABS. The country barely has electricity, the complex activity of building a rocket to Mars is far beyond them. South Africa during the aphartide era, has a better chance of reaching Mars.
1) the Soviets have adopted a hybrid market economy in the 80s, so what "communism" is and how it's perceived is not the same as it is in our universe
The "hybrid" system is state capitalism, the same as China does today.
2) The world went to DEFCON 2 in 1983, something everyone keeps continuing to ignore as a major development in the history of the show that might be impacting people's decisions
Yes, one of those decisions is not to have a communist government in Mexico. I doubt the USSR will complain. This is a two way street, which indicates that the spheres of influence are more solidified and less expansionist. A communist Mexico is literally a return to defcon 2. An intimate invasion of the US sphere of influence.
3) Reagan is no longer president and by the late 80s when Mexico elects Verdugo President Hart has adopted a more accepting foreign policy in direct reaction
Acceptance is one thing, cowardice and weakness is another. A USA that accepts Mexico into the sphere of the USSR is a country that does not have the power to protect its allies or itself. The simple fact that Mexico is in the Russian sphere breaks any trust with the capitalist countries of Latin America, Africa, Asia and Europe. If they actually accept this, this USA is weak. It's the only thing any country would see. Accepting a communist Venezuela would be acceptance.
4) Verdugo in OTL by the 80s was directing a merger of the Mexican Communist Party with more democratic socialist parties
It's less USSR more Yugoslavia. The USA killed Yugoslavia after the Cold War.
You seem to be operating under the assumption that everything in the For All Mankind timeline in the late 80s is the same as ours
You are operating on a very simplistic view of politics. Being a super power has duties and obligations, it's not just positive things. The first of these is to control your neighbors, your most intimate sphere of influence. If the USA cannot deal with Mexico, the country is not a super power. It's a powerful country, but the USA was that before it became a superpower. No country will look at the USA and think it is super power. No country will expect the US to use force, just words. Basically this is signing the death of the American empire. The European Union would have developed an army earlier, with France probably being the organizer of the European Union. Anti-communist Latin American countries will organize themselves without the USA, the same in Africa, Asia and the Middle East. Japan would become militarized, among other examples. Honestly, the simple fact that the USA accepted that Mexico was communist should be an entire episode, with the effect being the breakup of the American empire. With the USA accepting not to be the superpower on the capitalist side, but returning to its isolationist phase.
PS: another problem is the USA is liberalizing too quickly, when there is a hyperliberal phase you generate an aggressive reaction. As seen in the ussr, this america would have a trump or something like that. Furthermore, we have the issue of homosexuality in the rest of the world.