In my opinion the move to the new gaff has definitely had an effect. Like you say the old guard have been diluted by the new STH's and they just don't know the songs. I heard a strangled "Grand Old Team" against City at the weekend. The first time I'd heard it. I was encouraged by that, but it couldn't catch on because nobody had any idea there was any words after "Wooooaahh". The simplest way to sort this would be to let those who specifically want to sing stand together in the South/East corner. Make it explicitly clear that this is what is expected if you renew your season ticket there, and allow people to move out otherwise.
As someone said elsewhere it would only take a couple of hundred voices together to make sure there is a decent amount of noise that would just catch on. It happens in the Goal Line Bar before games, it just needs to carry on onto the terrace.
Infuriatingly the 'wall' got fucked up by the seat allocations.
I wish the club we re-configure but I'm doubtful they will.