But seriously, a recurring motif or element should be meaningful in some capacity, and not just there because. Nothing in storytelling should ever be there "because." Evangelion is not something to be emulated - it is sound and fury signifying nothing, and that is to be avoided.
Like, seriously. Even easter eggs and recurring visual gags. They should be referencing *something* even if it's just an artist's gag. But if you have to ask people to tell you what it should be, then it's not your gag, really, dig?