Re: Easter Eggs (SPOILERS)
The idea of Krypton as a space-faring civilization that eventually became insular, cutting off itself from it's many faraway colonies, seems almost like a reference to the Daxamites (Kryptonians only they are poisoned by Lead instead of Kryptonite) and also a bit of the DCAU Supergirl, who was a Kryptonian (or something ridiculously close) from another planet near Rao.
Oh, and here's another one I found that nobody else has pointed out yet here: At one point during the Metropolis sequences, you can see an ad for a "Utopia Casino". The Utopia Casino was a key location in the Superman Confidential story arc "Kryptonite" by Darwyn Cooke and Tim Sale.
Marvel. DC. Indies. Who cares? Can't we all get along?