I am of the opinion that Superman wouldn't know what to do with himself if Lex truly died. The same as Batman with the Joker- cruelty, tragedy, intelligence, insanity. Such are the things of legendary enmity.

And it is always better, stronger, and harder to let go of when it started out as friendship.

I agree with you- Lex Luthor is truly under-appreciated for his intelligence. That, and in cannon he's psychic... and they leave that out a lot, in the animated series. When he creates a clone, Kon-El/Superboy, using his and Superman's DNA, it inherits more of him than it truly does of Superman: in the form of a tactile telekinesis and extendable aura.