Actually, I think that Heinlein simply explores the questions raised by Nietzsche's writing. Stranger takes a look at the way the Ubermensch ("superman," the next stage of man) wields a power to change the world, whether he likes it or not; the world changes necessarily through the appearance of a transcendent, and democracy of ordinary people is little more than a way to retain order until the arrival of such an individual.
Starship Troopers, on the other hand, explores the other critique of Democracy as being inferior to a meritocratic system - also going with NietzscheNietzsche's ideas. That is, the power to alter the course of a society (i.e. voting) is not given freely, but deservedearned (in this case, through willing to put oneself at risk for the sake of others) . As such, the structure of society is never at the mercy of the lowest common denominator.
I tend to view Heinlein through the lens of Nietzsche, and I see his ideas as fairly consistent.