Modern comics have dealt with this issue of refusal to believe. Lois and Lex for that matter have unsurmountable, unbelievable evidence that Clark Kent = Superman but because he is so effective in his goofy persona that they just can't believe it. Morrison has done one better by actually having Clark become a costume of sorts where Clark slouches, stuffs his shirt, speaks an octive above his normal tone and wears tinted glasses to hide his eyes. Literally they are supposed to look related but not one, his take has at least made it plausable, with him even saying he wanted to make Clark a bit overweight so that way when people say "Where is Clark?" the thought is he couldn't keep up with Lois running after Superman.
As for Smallville, I haven't watched a lot of the tailend of the season after Justice but I have to say I was seriously impressed with the finale, the best episode to date for me. I loved him seeing the Superman costume and the dream of his flying around...it made serious want more. I actually can't wait for next season and that is a statement I haven't made about Smallville for a while.
As for his status, they've employed magic heavily throughout, it would only take a magician to wipe the world's memory of Clark as we see him to Clark as we traditionally know him to set things right. In fact Superman himself is very weak to magic, they could make Clark think of himself as the bumbling fool for the greater good. It wouldn't be too difficult to achieve given the ground they've built.