Maybe both would be good? I don't see why it has to be an either/or situation. Use unmanned missions where required or practical, and keep the manned misions going where feasible and best suited. Lets face it, the outer planets are a ways off yet in terms of manned flight, so there's nothing wrong with sending some unmanned birds out there for a look. I am involved with the JIMO effort now (Project Prometheus) and that has some real juice to it.
Long term, I agree, people are going to have to go there, at least for places where it makes sense to go. The opening up of new frontiers for exploration and development has been a common thread throughout human history. Its just a logical extension to off-world travel.
Both are good and desireable. Send a robotic probe first. If the results look promising, THEN send a human crew. It is the nature of humans to explore and colonize. The entire history of human evolution has been driven by the need to "see what's out there". It's why the first humans left their small communities and hiked over the nearby mountains, and why Columbus sailed over the horizon, and why Americans went west, and why we'll someday go to Mars...and beyond.
We have to get some of our genetic eggs out of this basket. We must be able to leave the "nest" and begin to move some of the industry, resource and energy production issues to a new playing field. And population will eventually be an issue, even if the Earth First crowd is wrong about it being a dire problem now. And one asteroid or mutated virus and it's all over. Unless we're somewhere else in survivable numbers as well.
There is an interesting article posted a few days ago by the SF author Spider Robinson (the original author, not, I presume, the poster)about this that touches alot of the attitudes and trends involved. The title is:
Why are Our Imaginations Retreating from Science and Space, and into Fantasy?
a robot probe is a tool. It can't replace the imagination of a human being who's on scene and really experiencing the reality. It can extend their senses and make them more capable. The object, however, is for us to be able to leave this rock and go elsewhere.
I'm an old school kind of guy. When I want to use nukes in space I want to use NUKES. I prefer Orion ;^>
Actually, Prometheus is excellent, from what I've seen. It does harken back to some of the earliest proposals in Von Braun's visionary stuff from the 50's and 60s, but there's nothing wrong with that, and the techniques and technologies have come a really long way. Do you know if they're going to incorporate some of the Russian powerplant stuff we got after the wall fell? I understand that was really good technology, reliable, robust, simple.
My only real problem is with the name. You do know what happened to Prometheus after he gave man fire, don't you? How's your liver? Who came up with that name?