I always thought the dynamic rested on the idea that Superman was bold, daring, and adventurous while Clark Kent was in most ways Superman's opposite, meek, kept to himself, and plain. I might not really call him bumbling, maybe just someone most would consider a sort of wall flower type. If Clark Kent is just Superman in different clothes then what's the point? Where's the fun in that?
It's a shame most actors seem to hate playing the fool as Clark Kent because I think it sort of makes the Superman/Clark Kent dynamic and showed that at some point even in the life the world most powerful man he isn't always THE man. Even he's got bosses he has to answer to in Perry White and office bullies in Steve Lombard.