I'm wondering if, given the all-or-nothing nature of nuclear warfare and the fact that systems weren't 100% reliable, the Soviets or US decided to point multiple missiles or bombers at the same location to ensure it wouldn't escape destruction. Especially in regards to major command and control locations like Moscow or DC.
Massively so, yes. They desired certainty of destruction — which only happens if you target a lot of weapons and weapon systems at the same targets.
One very nice illustration of this: Sec. of Defense Robert McNamara asked in 1961 what their targeting system at the time would do with the city of Hiroshima. The response he got back was that it would recommend three 80 kiloton nuclear weapons destroy the city. That's pretty redundant, given that one 15 kiloton weapon effectively incapacitated the city in 1945.
Most certainly. Both sides figured that 1) the delivery systems were not entirely reliable, that 2) the enemy might have some means of defence (particularly against bombers), and 3) some of the forces might be destroyed in a surprise attack.
/u/restricteddata is probably the guy to give the best answers here, but for quick reply, here's two estimates.
In 1957 Gaither Committee report "Deterrence and Survival in the Nuclear Age" to Eisenhower, the basic assumption was that one needed four airplanes per target to give a reasonable chance of destruction (Kaplan, F. 1991. The Wizards of Armageddon, p. 151).
And /u/restricteddata has this great blog post about the first U.S. nuclear stockpile requirement from 1945: http://blog.nuclearsecrecy.com/2012/05/09/weekly-document-the-first-atomic-stockpile-requirements-september-1945/
It assumes that the "incapacitation" of first 15 priority targets would require 39 detonations in total, and that 48% of bombs would actually detonate on target (the rest being e.g. not available for loading on bombers, the bombers having technical problems or being shot down enroute, the bombs missing, or bombs being duds).