You still need enough energy to keep a large ecosystem going for thousands of years (at least), with no solar power available. Then remember you have to schlep that power source and fuel with you.
The problem here is the distances involved. I love the motto by Physicist; "The universe is the way it is, and not how we would wish it to be".
It appears that interstellar travel is a feat that is incredibly difficult to undertake. I read about Bussard Ramjets or generation ships and I think of the vast expenditures that would be required with zero return for the society building such. Not withstanding the engineering hurdles that would be required. We last walked on the moon over 30 years ago now and it’s only approximately 240,000 miles away orbiting our own planet. The nearest star is 4.3 light years away giving it a whopping distance of about 25 trillion miles. We haven’t even solved the entire engineering problem for a trip to Saturn, much less star flight.
Even if you take into account the Lorenz Transformation and you were able to build a ship that would travel at near "c" (the speed of light). Would anyone want to undertake a journey where they would know for a fact that not only everyone they knew back home would be dead, but their entire civilization may be also? Even if the journey took only 20 years "ship time", would you do such if you knew 20,000 years would pass back on you home planet? (These numbers I am pulling out of the air. They would be different depending on how close you approached c and how far you traveled.)
Thusly we are left with (at out current level of technology and understanding of physics) radio. SETI is just that, looking for a civilization emitting radio wave into space not unlike what we are doing ourselves. The rub is that it is terribly difficult to detect those emissions at the vast distances of interstellar space. To further complicate the picture is what frequency do we look for, where do we look, and for how long at each location. Let us surmise a civilization is looking in our direction at the frequency of one of our BMEWS sites. As our earth rotates, the beam into space will also move. They would have to be looking for possibly 20 to 24 hours to "see" us if they happened to look at just the wrong time. This is why our current SETI program is looking at multiple frequencies and the same locations over and over. The big question is where, what frequency, and for how long at each location. The other problem is radio still travels at c. So even our emanations have encompassed an area of about 120 light years in diameter. If a species happened to be looking in our direction whose planet was more than 60 light years away, they would not even be able to detect us yet.
Do I think SETI is a waste of time? Since I "do" SETI with a radio telescope the obvious answer is no. However, I cannot even predict if or when a signal may be discovered. The WOW signal is still intriguing, but it never repeated. IMHO, SETI is a win win science. If we are alone or find that we do not "see" anyone else out there; that in itself is profound. If we do see someone there, this too is profound.
So if we do find that extremely narrowband signal heralding the fact we aren't the only intelligence in this vast universe, I think it would further our understanding of our relationship with this universe. With C being the fundamental limit (speed) of communication, "talking" with another race would be quite impracticable. Not much of a conversation if you have to wait 3000 years for a reply to your hello. Still we would know as a species that we were not the only organisms contemplating the existence of the universe. Finding another intelligent race would definitely redefine our place in the universe.