Vietnam was mistake for everyone. But it had very little impact on the Soviets, since Vietnam did not turn into a bunch of Soviet hating fanatics as Afghanistan did. There was no Vietnamese equivalent of the Taliban.
The Russians sent money and weapons to the Vietnamese, but not many troops.After the War was over, Vietnam had a minor spat with China. Cambodia was ruined by the Vietnam War, far more than Vietnam itself.
Vietnam was the dumbest thing the US did except the Civil War. It looks like Iraq will turn out to be dumber still, but Vietnam changed the US for the worse in ways that Iraq did not, because of the massive number of troops that were drafted and forced to serve there
Had the US just allowed elections to unify Vietnam under Ho Chi Minh, I am sure that today, Americans would be buying Nikes and Reboks made in Vietnam. The average Vietnamese family would still be poor, but there might be more Vietnamese. It is possible that Vietnam might have been more likely to have decided to do what China did and become capitalists.