Marxism is, as I am sure you know, an ever-evolving theory. If we look at these states dialectically, we can see unresolved contradictions that did indeed lead to collapse in the case of the USSR, but we can also point to rapid progress and enlarged social safety nets.
I believe by "Libertarian Communism" you are referring to a far more limited government, yet you also appear to desire an elimination of money on an almost immediate timeframe. You also quote Marx, in the Stateless, Classless, Moneyless society as well as from each according to his ability, to each according to his needs, yet reject Marx's descriptions of what those accomplish and look like.
Honestly, I believe you are making the same philosophical error as the metaphysicians, looking at a concept from one side devoid of the other, at a static, fixed point, rather than dialectically as it changes and resolves its contradictions. The USSR was making advancements, until it killed itself. We should learn from this, rather than reject it wholesale.