VASIMR certainly has a lot of potential, but we are lacking the power source to drive it at reasonable power. Combined with photovoltaics, it will only open up the inner solar system, as the intensity of the sunlight decreases at the square of the distance to the sun. At mars, the intensity is already between a third and half of that near earth.
Unfortunately, everything that contains the word "nuclear" cannot be used for political reasons. There are even protests every time a probe uses an RTG. We would probably need something like this to make the best use of VASIMR.
With regard to the "age of sail", I would really like someone to develop solar sails and test them in space. Yes, I'm looking at you, NASA...
Prediction is very difficult, especially of the future. - Niels Bohr