Well, Sir Arthur draws a comparison with the exploration of the poles.
First, there were the early 20th century explorers (Scott, Amundsen, Peary, Charcot) who went to explore with boats.
Then, the poles were left alone (ok, there were 2 world wars in the mean time) for 50 years until they were reconquered with....the planes.

I believe, if we want to leave Earth Orbit again, we'll need to develop a totally new propulsion mean; a mean that could be useful for the entire solar system. And once operational, every world in the solar system will become accessible.
I don't think we should concentrate on the planetary goal, but rather on the traveling method.

Raoul