Yes, NATO is still vita for the world's security, because the world cannot be too vigilant in preventing another world wide conflict. As weapons become more and more destructive, it is all the more important that nations communicate, rather than throwing bombs. World War Two was not that long ago, and neither was Vietnam. NATO still has a purpose.
A support hierarchy is needed so that policies and guidelines can be written and set. I believe NATO is vital because there is a significant amount of countries that hold different values and opinions. There needs to be a stage set for the countries to gather and discuss these differences. Differences lead to all sorts of problems and setting a stage where each county can come together and set fourth policies that they all can agree upon is a necessity especially when weapons of mass destruction is involved.