Lynn, I'd like to comment further on your first point.
1) A lot was made of the sentence "The morning star is the evening star." (Both refer to the planet Venus.) Since this is the L&C board, I can make the exact same point with the sentence "Clark Kent is Superman." If the meaning of a word or phrase is its referent (that is, the object in the real world to which it refers), then the sentence would always be about as interesting as "a rose is a rose"; that is to say, it would be a straightforward tautology. But as Lois Lane's reaction in the vast majority of Revelation fics would attest, that is clearly not the case.
I respond to this point thusly.
1) The morning star (Venus) and the evening star (Venus) are the same physical entity, but they are referenced differently according to the context. I suggest that they are, in fact, different "things" not because they are two different heavenly bodies but because they are viewed differently. Venus in the morning has an identity that is separate from Venus in the evening. Ancient cultures without the astronomical observational equipment we have would have referred to the "morning star" and the "evening star" as two separate phenomena because they didn't know they were both the planet Venus. The context identifies them.
2) Similarly, the statement "Clark Kent is Superman" is correct when we think of the (fictional(?)) male humanoid who variously identifies as CK or SM but who does not identify himself as both at the same moment of time. Because he keeps the public recognition of either entity separate, we can state that Clark Kent and Superman are different entities - because of the context, you see. Superman does not interview people or correct Lois' spelling. Clark does not lift space shuttles into the sky, nor does he catch bullets in his bare hands (not where anyone can see it, anyway). Because the Clark/Superman entity keeps the two identities separate, we can legitimately say that they are two different beings, even though we know that "Clark Kent is who I am. Superman is what I do" because we, as fans and readers and authors, are inside the mythos.
All this is not to say that I disagree with you, simply that in such discussions there are multiple points of view. One might make the argument that neither Clark Kent nor Superman exist as beings in the Superman fictional world because the appearance of one cancels out the existence of the other. They cannot exist simultaneously in the same space-time continuum. (Alt-Clark doesn't count - he is a distinct entity/being/identity all his own.) It's almost as if one is matter and the other is anti-matter, except there's never a catastrophic reaction because they never make contact with each other.
Mind-bending, isn't it? My wife thinks I'm a little nuts to even think about stuff like this. Of course, she's a Twi-Tard (a
Twilight movie franchise fan), so there's that fictional(?) world too, where she can tell me all about the different characters, their motivations, their ambitions, their frustrations, and I just can't get past "the vampires sparkle in sunlight."
Your observation about Superman at an outdoor cafe table left out Spiderman, Wolverine, and Cyclops. They're obviously debating the question of our existence.