I'd've also loved to have seen Luthor in the TV show.
He could've been a behind-the-scenes villian, as the creator of the giant freezer that took Superman's powers away, for example. Luthor might not have wasted his time robbing banks, but his minions would only have been too happy to try to take advantage of Superman's weaknesses at that point.
They could even have used stock footage of Luthor at the end of his episodes reading a paper or listening to a radio broadcast of Superman getting the upper hand saying, "Curses! Superman still lives! SOMEDAY, Man Of Steel! Someday..."
Every season's finale could have had Luthor thrown in jail again, too!
Most episodes would only have needed little tinkering to have been Luthor plots to destroy Superman.