In this day and age, it is hard to be optimistic about humans ever visiting other planets in our solar system. There are major technical, medical and psychological problems that have to be overcome and at the present time, no one really knows how to solve these problems. There is also the rather pragmatic issue of how we as a society should pay for such a program. Today, NASA is under relentless pressure to down-size and cut research budgets and staff. We will never go to Mars if NASA has to be shrunk to 1/2 its present size. Such an undertaking is very expensive and requires lots of talented people to pull it off, not fewer people and smaller financial resources.
I think we will just have to wait and see what happens when the Space Station is completed, how it is used, and how we all feel about THAT investment. You should be forewarned, however, that putting the Space Station together will require over 2000 hours of astronauts in spacesuits. One single misstep, one death in space, and our Nation's commitment to space will be over, under the pressure of many Congressional investigations and the usual political haymaking that goes on. When a US soldier, trained to take risks and willing to face death, is killed in Bosnia, this produces a major calamity in the US. How much more of a calamity when a civilian astronaut is injured or killed in space!
Also, the space shuttle fleet is getting very old considering the tremendous abuse it gets. Recent estimates say that we will loose one more shuttle in the next 700 launches or so. Statistically, this could happen with the very next launch. If this happens, no one will call for building a replacement shuttle, and everyone will probably call for the shuttle fleet to be stopped in its tracks. If the Space Station only consists of a few parts by then, there will be a domino effect and I can't believe that the Space Station would be completed. Some will find this a blessing in disguise, ending once and for all a major engineering project that has not had universal support among scientists and many members of congress.
Also, a recent American woman astronaut was recently 'abandoned' on the MIR space station while the entire shuttle fleet was grounded because of a potential problem with erosion in the solid rocket boosters. Her stay has been extended at least 6 weeks until August, 1996. Think what would happen if the same thing happened while 10 - 20 people were aboard the Space Station? The point is that, space exploration is a very risky business where death has to be faced as a real possibility the longer you are in space. Are we really prepared to watch this played out on our nightly news, and then wake up the next day feeling that space exploration is still 'worth it'?