I think the shuttle procrast is also a bit of `show´ to the audience, since 4-th of july is also Independence Day. That way they got more attention from the public audience who fund the space program.

The 3-stage approach perhaps isn't any good idea after second thought, since there is no benefit for this approach (see the mentioned thread in the 1st comment: the problem is how to get rid of the velocity gain when getting back from the moon to earth).

Remains the question however: why not undertake that journey together with other nations?

It seems that China wanted to join the ISS, but USA was against that.

Space travel is expensive as it is and apart from scientific knowledge, there is no way of gaining something in the short terms from space exploration (even if new materials can be minded on other celestial bodies - the costs of bringing those to earth would be immense).

Not that I'm against space travel, but the question is wether it's worth the immense costs.

When those costs are spreaded amongst several nations, it becomes more affordable, and international cooperation is a good thing.
If we want to solve the problems on earth (which should stay our main priority), such a joint space program would realy pay off.