The journey that begins with SIM will eventually lead us to travel to nearby Earths. The first visitors will be robotic and they will be sent to worlds that are discovered by SIM. The closest solar systems will still be unimaginably far away, even when compared to the large distances between planets in our Solar System. For example, Neptune, the farthest planet from the Sun, is located 30 AU from our star. In comparison, 1 light-year is equal to 60,000 AU! The closest star system, Alpha Centauri, is located at 4 and 1/2 LY from us, or 270,000 AU. The vast emptiness between planetary systems presents a daunting challenge.
However, even now, there are those who are proposing ways to cross that ocean. The following is a link to an article by Ian Crawford. The Reference section at the end of this paper is a very handy guide to the literature of interstellar flight.
Comment on "The Far Future of Exoplanet Direct Characterization" - the Case for Interstellar Space Probes
This paper reviews some of the technical objections to interstellar flight and makes the case that these can be overcome. Crawford points out that any future detection of biosignatures in the spectra of nearby Earths will inspire the development of the technology required for such flight.
I would add that the discovery of the mere existence of nearby Earths will inspire the creation of advanced space telescopes that will be able to detect those biosignatures. SIM is the only mission that is designed to detect those nearby Earths. It is the crucial 1st Step in the long road that will lead us to explore those nearby New Worlds, both by proxy and in person.