It's been said before that a solar sail could be used for solar and extrasolar missions - if you aren't in a hurry.
However, as you can't spell solar sail without the solar part, I'm wondering if you could expect to get reasonable propulsion through the universe once you are lightyears away from the sun.
It seems that eventually the propulsion coming from the sun would die down, and all that would be left is noise coming from other sources, all trying to push you one way or another.
Wouldn't a solar sail's value diminish greatly once you are in the middle of nowhere?