The Luthor in the Superman animated series seemed to view masterminding crimes as a game/sport/hobby. Something he did for fun. I think one of the real world reasons for Luthor (throughout most of the silver-age) wearing only his prison uniform was the comics code authority. DC could have been afraid to put Lex in a suit. Might have made him look like a businessman. I believe the comics code forbade depicting government/law officials & businesspeople as being crooks.
Yeah, that's how I see Luthor as well.. He's brilliant enough to make billions legally, or semi-legally. Why commit acts of super-villainy for profit? I do think that his acts of mastermind villainy should be something he does to entertain himself, rather then something he does out of necessity. ...Which frankly, only makes it more evil.
...And expanding on that, what if Luthor's motives for wanting to destroy Superman wasn't really hatred for what Superman represents? What if, instead, he sees Superman as the ultimate challenge for a being of his intellect? Sort of a "I never knew failure until I faced Superman.. I've never been challenged like this."