As I just mentioned in the alternate running mates thread, having anyone other than Agnew as Nixon's VP in 1969 is going to cause significant changes in the history of the space program. Agnew was one of the greatest supporters of the space program since NASA's foundation, and his enthusiasm was a factor in the Space Task Group adopting a wholly unrealistic model of the way forwards for human spaceflight after Apollo. An alternate Vice President likely does not feed back into Paine in the same way (and may even push Nixon to replace Paine), which will have a significant effect on STG planning. This could significantly accelerate "official" adoption of Shuttle or lead to a commitment to build a space station with Shuttle, for example.