mike, as southern vietnamese, I have no problem at all to see Vietnam to ally with America and Japan. most southern vietnamese would think the same, I bet. my father served in the south vietnamese navy, that fought side by side with America during the war. my countrymen in the north see thing differently of course, they would rather see our country with Russia.
So we are familar with one thing or the other. I think Russia is not an option, because it relies on China for money, investment and friendship. so it is only America.
the problem is, before making any decision, be alignment with a superpower or developing indigenous nuclear weapon program, we need to consider possible reactions of China and Russia. and that is somewhat unpredictable.
worst case scenario: Russia stops all relationships, and China starts an invasion to test America. we face economic sanctions.
besides, Vietnam is a bit sceptical about alignment. in 1979, China started the ground invasion because it feared a two front war. the Soviets did not intervene. in 1974, China started the invasion of Paracels, the US did not intervene, either. in both cases, Vietnam had defence treaties with the Soviet and America. You see, back then our defence treaties were not much worth. China has nuclear weapons, that hindered the superpowers to intervene in favor of Vietnam. Nobody wanted to risk a nuclear winter.
nevertherless, I believe sooner or later, we will face the decision to alignment and nuclear armament.
Good to know bro. Its indeed a tragedy that the south(vietnam) together with U.S lost the war to reunify vietnam under a democratic government. This is mainly due to China and Russia support to the communist Viet cong rebels. If not for that massive support, the U.S and south Vietnamese troops would have crushed the communist in the north in just about a few months. Vietnam has China and Russia to blame today for its current communist government. Had it not been for this, then Vietnam would have long been a U.S/Japan ally, which would have made things easier for Vietnam to face China currently.
However, due to Vietnam still having a communist government, it still guards its power more preciously than the Country. Which is understandable since most one party state will rather keep their power by all means, regardless of what it might mean for the country. The party always comes before the state. So obviously the Vietnamese government will always be cautious not to get too close/ally with the U.S since it fears for its own power(thinking the U.S might use the slightest opportunity to forment trouble to topple them for a more pro U.S/western government). Similarly, the VCP also has members who are more pro China or value a peaceful negotiation/setlement/ties with China. since they see China as less a threat to their own power than the U.S. So this makes it more complicated as there are 2 sides in the party fighting for which policy should be adopted especially during crucial moments of crisis.
As for the point that the U.S and the Soviet Union didn't intervene to protect Vietnam/honor their agreement during Vietnam's conflict with China in the 70s. Well as you yourself said, you cant blame them that much, Since its true China was already a nuclear power back then. So theres no way either the U.S or U.S.S.R could attack them. It would have mean a nuclear winter in Asia. So obviously they didnt intervene in fear of escalating the situation. Moreover back then Vietnam was also hostile to the U.S, so the U.S had little incentive/reason of helping Vietnam unlike today. Even so, don't expect the U.S and China to engage in a direct open conflict, it just isn't feasible, as both have too much to loose/MAD. But the Vietnam allying with the U.S can sure make China think twice about its actions with Vietnam, thus be less agressive while trying to lure Vietnam away from the U.S.
However, your last point is a no no for Vietnam. Vietnam seeking a nuclear weapon will be the biggest mistake it can make, since it will draw the whole international community to condemn and sanction it. Imagine a situation where the U.S/E.U/China/Japan sanctions Vietnam. Vietnam will be totally isolated and will go back decades behind, which will all but erased all the progress you have made so far. Moreover in this situation, China might even attack those facilities since it will consider it as a threat to the region, and no single country will raise a single finger/complain about that if it did.
That's without talking of the reaction of other ASEAN members, who will all condemn and even sanction Vietnam as well. So it will all but criple Vietnams economy. It isn't worth it one bit.
What Vietnam needs to do is to calibrate its foreign policy very carefully, prioritizing its ties with the U.S while at the same time letting China know it has got options, this will make China to at least take note and be more willing to seat on table and negotiate with Vietnam on the islands issue and not take any more agressive measures. Overall, a peaceful solution/or even share of resources/joint exploration of the region/islands will be the best solution IMO. time will tell anyway.
All the best to Vietnam and its courageous people.