To be honest, even the glasses and hair curl are a huuuge stretch. Especially for anyone who's around him for any amount of time. So, really, if we can suspend our disbelief enough to believe that a pair of glasses make you look completely different even to the love of your life, well... <shrugs>
Of course without the glasses we'd lose awesome exchanges like the following.
"If you wanna kill Superman, I don't know why you're going to Smallville or 1966."
"She doesn't know yet. Oh, this is good. This is really good. Um, Lois, did you know that, in the future, you're revered at the same level as Superman? Why there are books about you, statues, an interactive game. You're even a breakfast cereal."
"Yes. But, as much as everybody loves you, there is one question that keeps coming up: 'How dumb was she?' Here, I'll show you what I mean. Look <puts glasses on>
, I'm Clark Kent. <takes glasses off>
No, I'm Superman. <puts glasses back on>
Mild-mannered reporter. <rips them off>
Superhero. Hello! Duh! Clark Kent is Superman. Ha, ha, ha. Well, that was worth the whole trip. To actually meet the most galactically stupid woman who ever lived."