Good answers, all.
Sure, Vito would take paternal pride in Senator or Governor Corleone, and it might take some of the tarnish off of him (although, as Oli said, Vito didn't seem to care much about America or American values). But, I've always believed that Vito would want Governor Corleone or Senator Corleone to work for legalizing gambling in New York or the US as a whole, which would vastly expand and legitimize the Corleones' dominance in illegal gambling. Of course, illegal gambling would continue, as it does today in states that have casinos and offtrack betting. Sonny would be the head of an ever-decreasing "olive oil business" and provide muscle for Michael when needed. This would set up resentment/rivalrly between the brothers--an interesting situation for a new GF movie or book.