Heinz is still a dump and the only reason it sells out for the Steelers is because there is a genuine, cult like, mentality for the team. People show up and just sort of sit there.
I went to ND 2013. No atmosphere at all. Not sure what you saw but it felt like a sterile NFL game.
I wasn't at the Notre Dame game; I only surmised the atmosphere from what I saw on TV, this board, and what was said by people that I know who went to the game.
If it was as sterile as you're suggesting, that's probably because of Pitt's 4-5 record going into the game. It's why I didn't go.
I've said this before: I've been to Pitt games at Louisville, Notre Dame, Michigan State, Nebraska, and Navy. The only stadium that's made me say Heinz Field stinks is Navy's.