I think plenty are there to enjoy the atmosphere, but not necessarily add to it. I wish everyone was there to replicate the London Road but realistically that's usually the ones standing at the back, and a peppering of fans sat beneath when the team lifts the atmosphere with a goal, corner etc.
You're right there are plenty in the North Stand who already join up with East Standers at away games and all sing together. Another example that if all those fans tried to rendezvous in one area, whether that be North, East or South it would be impossible due to existing ST holders.
New stadium, if there was an unreserved area behind the goal, whether safe standing or not, I would go there every game and probably help create an Ultras style atmosphere to grow and give my help to an existing group.
If the club didn't organise an unreserved area, I'd probably get a ticket near the away section for the back and forth atmosphere, and most other young ones would probably do the same.