I think there were clear differences between Vietnam and the Cuban crisis.
Rather worrying when you compare these differences to the Iraq war. (No danger to America and forged intelligence as part of the reason for going in.)
As phrased in your post, there is nothing contradictory in those two lessons. They could actually be complementary, since fighting a war all out in places where one is wanted (as across the plains of Northern France) is almost an ideal situation. Even phrased differently, those lessons simply approach different aspects of policies to conduct a war.
I am not a big proponent of “the lessons”–although I think I know which “lessons” have been expressed over the last 30 years–and you may have a point that the “lessons” can be illusory. However, I think that studying the follies of the past can provide education, even if we can never get our leaders to actually learn anything.
Another vote for The Fog of War. I ordered the DVD. Eleven lessons. Good stuff.
Do not lie to precipitate or escalate a war; lies are superfluous if there is a compelling need for combat, and self-destrutive if there is not.
Another lesson is that in fighting a war such as that, you tend to give more power to the most radical, extremist, and sadistic elements of the opposition. Thus, if you lose then you likely end up with a much worse situation than if you hadn’t interfered at all. While one can obviously never know for sure, I just can’t imagine that the genocide of the Khmer Rouge would have happened, at least to nearly the extent it did, if not for our “help”.