I clearly don`t see Superman as a disguise but a symbol. It`s the sum of Clark`s childhood + Kryptonian powers. Clark is free to use his powers to help people around. He says on Man of Steel # 2 something like "For the first time, i feel free. After been hiding for so long, it`s nice to fly in the open." Superman IS REAL. He doesn`t change his manneirisms, pretends to be strong or whatever. He is strong, confident, etc etc etc.
In fact, in post-crisis, Smallville Clark and Metropolis Clark are the same person. It`s just that in Smallville, Lana and the Kents know that he is also Superman. But to Pete and others they are the same. To them, that Clark went to study journalism and works at the Daily Planet. Just a normal human being.
He is both Superman & Clark.
It`s not really that hard to understand.
TO ME, ALL IN ALL, THE SECRET IDENTITY DEPENDS ON WHO HE IS INTERACTING WITH AND WHO KNOWS HIS IDENTITY OR NOT. Generalizing stuff is never a good idea to explain a character so complex and multi-layered like Superman. Things are just not that simple that you can summarize everything in one phrase: Clark is the disguise/ Superman is real or Superman is real/Clark is disguise. The truth is: IT DEPENDS!!
My interpretation of Post-Crisis and my interpretation of Superman overall is that Clark is Kal-el being human, living a normal life. It`s the one who was raised by the Kents and moved to Metropolis to work in the Daily Planet and to preach wisdom and truth. And Superman is Kal-el being heroic and using his powers to do good, a man of action, using everything he was taught during his childhood. Both are real, both are disguises in some shape or another, both depend on whatever circunstances, interaction etc etc, if that makes sense.
I personally like the way it`s show in Superman for all seasons. Clark in his childhood is reserved, not the total jock, high-school star, as he was shown in Man of Steel. I`ve never liked that also.