I’m pretty sure Lucas said somewhere that the pod race had its origins in an abandoned idea for the first film. Makes sense with Lucas’s love of racing.
Also, doubleofive is spot on with the subtle narrative going on with Luke’s piloting experience on Tatooine naturally transitioning into the trench run.
Kind of annoys me when people make fun of the exhaust port being a weak point when the whole idea is that a normal pilot, even using a computer, would never have made the shot. It wasn’t as glaring an oversight on the Empire’s part as some people try to make it out to be.