Palpatine and Sidious - should've been clones and should've been the real catalyst for the clone wars - the whole "good and evil twin" cliche taken to a Star Wars extreme.
Obi-Wan Kenobi should have been OB-1 Kenobi (a clone designation - a name old Ben had not heard in a long time!)
Midichlorins should've been a psychedelic drug that makes you feel "closer to the force" whilst under its influence.