Michael Rafferty, Deputy Program Manager for the International Space Station, tries to pitch Using ISS for Human Exploration Beyond LEO He describes missions around the moon, near earth objects (asteroids near earth) and Mars missions. All of these things could also be done without the ISS, but since it is up there already it could be used where appropriate.
There is an emphasis on solar electric propulsion as well and there are other propulsion and power systems which could work. The panels like what they propose are on the ISS but those are heavy and do not provide as much power for the weight. It looks like because of the weight of what they are proposing they would need multiple launches and assembly in space. More launches and more work in space increases the costs of the missions. The pictures are pretty though.