Yup, and to your point lelak the flagship Superman title was selling close to 1 million copies in 1960, and Mort's other titles were in the 500k range. I'm sure there was some residual boost from the 50s TV show, but you have to give Weisinger his due.

As far as his "planting" letters, while I'm not saying it never happened, I do think that's been overblown. With that kind of circulation, he must have had hundreds, if not thousands of fans writing in every month, and built up a stockpile where he could always find something to suit his whim. And to be fair, as we've seen, not all of the missives he printed were complimentary.

"As for contentment, that is a myth.  Give a man everything he wishes and he will be unhappy, because he didn't wish for more; give him more, and he will die of his worries.  Only a turtle, asleep on a sunny log, knows contentment!"
-Merlin to Prince Valiant

            Hal Foster 3-7-43