The joy doubles. Not only does Sanjaya rejoice at the memory of the dialogue — he is also overwhelmed each time he recalls Krishna's Vishwarupa, the cosmic form revealed in Chapter 11. That vision of infinite mouths, infinite eyes, the entire universe contained within a single being — it left a mark on Sanjaya that does not fade.
Amazement is the word Sanjaya reaches for. Not understanding. Not analysis. Amazement. Some things are too vast to be reduced to comprehension. They can only be witnessed, remembered, and wondered at. Sanjaya does not claim to understand the Vishwarupa. He simply says: the memory of it fills me with awe, and the awe does not grow old.
The phrase 'punah punah' — again and again — mirrors 'muhurmuhu' from the previous shloka. Together these two verses paint a picture of a person whose inner life has been permanently enriched by what he witnessed.