A little reflection shows the discussion here has changed once we moved from solar system exploration (probe vs manned) to interstellar missions. This is to be expected, once interstellar travel is possible, no matter how primitive, both the challenges and payoffs are different. But the basic problem remains: how do we maximize the overall effectiveness of the entire program.

In an interstellar scenario, postulating spacecraft traveling at essentially non-relativistic speeds (less than .5c) I suspect a truly long-term program conducted by a mature Terran civilization seriously interested in exploration of the nearby space would do it thusly.

Automated probes would first be dispatched to selected stars on flyby missions and they would primarily be designed to eliminate these worlds from further exploration; i.e., we would attempt to winnow down the list of candidate destinations. These spacecraft would boost up to maximum velocity, their orbits planned so they would flyby several stars on the way out, (picked to be roughly in a radial direction away from earth), cursorily examine them and beam back reports to earth.

Stars of particular interest located during these preliminary surveys would merit closer inspection by more elaborate robots, designed to decellerate at their destination and conduct a more detailed survey, perhaps by slowly maneuvering in the distant system, and reporting the results home by radio or laser.

Stars that looked really interesting in the close up survey THEN might merit the sending of manned crews to do more detailed surveys, or even colonization. This would require either very advanced propulsion, very long-lived crews, on board "ark" communities, or some kind of suspended animation techniques. Perhaps a combination of several of these. Like the precursors above, these are one-way missions...

Assuming no technological breakthrough occurs which makes the initial missions obsolete (arrival of the first robot probe finds a thriving Terran outpost when it gets to its target!) this method postulates a long term exploration program conducted on a truly long term basis. It means thinking way ahead, devising a strategy that might not payoff for centuries. If interstellar travel is going to be a hard as we think it is, it would be wasteful to send a human crew to, say, Proxima Centauri, where it might find nothing, when we could for the same cost explore a hundred worlds and possibly find one that might make it worth our while to send a whole fleet of manned vessels, with crews ready to move in and start sod-bustin'.