Not sure it was corruption per se, but everyone was making a profit, military was getting all the 'toys' they wanted. Also some 'corporatism' - in the sense that departments tend to grow and keep finding reasons why they should get more resources.

As far as a 'free' press', given that this overestimation was also to the advantage of the Soviets, I have to wonder if a Western reporter (or, well, really, any reporter) might have gotten legit defense information from the USSR - without being charged for spying.

The Sovs were far, far behind the West as regards telecoms (so if Moscow was hit in a first strike, they had no way to be sure a retaliatory strike ordered in Moscow might be carried out - so they relied on signal rockets, with no way to recall an order once one was sent. See David Hofman's "Dead Hand"). The TL;DR is that they were terrified of what the crazy Americans might do - so it was important that we really, really believe that a retaliatory strike would be overwhelming.