The theme music on World 7 is pretty hip. It's got a little bit of swing to it. 
Where do you think Bowser gets the means to employ all of these goombas and koopas? And what about all the airships he has? Does he build them himself, or do those get contracted out. 

I guess money is pretty easy to come by in the Mushroom Kingdom, now that I think about it. 
Hell, it practically grows on trees. You find gold coins floating in air, frozen in blocks of ice, and hiding inside of bricks. 

You'd think that would devalue the money, though.