Many technological advances derived from space exploration have aided mankind, including advances in medicine, computers (the thing with which you typed this question!), cell phones, microwave ovens, plasma screens, textiles, lasers/motion/radar detectors, etc. There are many links on the 'net that describes these in detail, but this one gives a simple, albeit brief, list: http://www.thespaceplace.com/nasa/spinoffs.html .

So, "yes", space exploration has been worth the expense and effort,
assuming you consider the aforementioned improvements worthwhile,
yet, at the same time, perhaps, "no", as mankind's current problems outweigh such:
the current budget is about USD 20 billion and expected to grow
(ref: http://www.nasa.gov/pdf/382362main_40%20-%2020090801.1.mars2019.pdf (article from 2009)).
Considering that medical health care costs run nearly USD 5 billion per DAY
(ref: http://www.chcf.org/press/view.cfm?itemID=119975 (article from 2006)),
USD 20 billion seems like a drop in the bucket!

Not only has the cost been worth the results the exploration of space is a healthy endeavor for humanity.
Human-beings are explorers by nature, its in our genes to explore the unknown.
Through exploration we have made our greatest discoveries and our greatest strides forward as a sentient being.
http://www.thetechherald.com/media/images/200902/milkyway_4.jpg
What we have spent on space exploration is a merger amount when you compare the benefical technologies that have been a direct result of our infant space exploration since Sputnik.
Our endeavors to explore space beyond our own planet requires us to develop new technologies which are adapted to making our lives here easier. The list of technological advancements is vast and growing everyday due to the space program.
Many of the environmental concerns that exist on this earth would not even be known to us had it not been for our venturing off this planet into space.

Look at the Hubble Space Telescope as an example, it has completely changed our understanding of the universe in the short time its been in service, imagine what a telescope on the moon would provide, being shielded for solar and earth radiation it would have the potential to see even further into the universe.
Another benefit is the increasing willingness of international cooperation toward space activities, this cooperation generates goodwill among nations that otherwise manifest hostilities towards one another.By the pooling of resources such activity cements bonds of friendship and communal achievment, which has to be a good thing.
Here is a link to a wealth of the benefical spinoffs that have come from the space program,
http://www.stars4space.org/Benefits.html

It is said by many that the pictures taken during the apollo missions such as this one,
http://llamabutchers.mu.nu/Earth%20from%20Moon.gif
sparked the environmental movement on earth, these pictures were awe inspiring at the time and caused people to realize what a fragile but beautiful planet we lived upon and instilled a sense of protecting it in many minds.

We shall survive or perish according to our stewardship of our home planet, this is a given regardless of our exploration beyond the earth.
If we fail to maintain a healthy earth then whatever we do in space will fail as well.
We must continue to overcome our earth bound problems, but we must also continue our exploration into the great cosmos, it is what we are at our core.
So to sum it up I would have to say, Yes we must continue to persue our exploration of space, it is vital to our well being and I think this quote sums it up quite well;
__quote
Exploration serves a purpose. It expands our awareness and conception of the possible.
__/quote

http://www.youtube.com/watch?v=5umfWJnZyco

http://www.youtube.com/watch?v=UuhDDx49TTw

To quote Tasmin Archer from her 1993 hit single
----quote----
have we lost what it takes to advance?
have we peaked too soon?
if the world is so green
then why does it scream under a blue moon
we wonder why
If the earth's sacrificed
for the price of it's greatest treasure

and when we shoot for the stars
what a giant step
have we got what it takes
to carry the weight of this concept
or pass it by like a shot in the dark
miss the mark with a sense of adventure

don't blame this sleeping satellite
----quote----

I've never really understood why we stopped manned space exploration. We live surrounded by satellites looking down on us , GPS, Weather, Imaging etc. Have we become so seduced by the benifits of watching ourselves from afar that we've forgotten to look out from the earth, to the planets and then to the stars. Yes Space exploration is expensive... but the Joint Strike Fighter project is around the $256 billion mark. Combine that with the cost of the stealth fighter/bomber and most people would prefer the money spent on sending men to the moon and on to mars. It would certainly have been more productive to do that.

I'm going to take the tack that we would be worse off without the space program. It has done far more good than harm, it has created more wealth than it has ever cost us to explore space and without the goal and desire to explore our universe what are we?

Thousands of inventions, thousands of lives saved.

Money well spent

Check out NASA in your life for all the latest news and inventions
http://www.nasa.gov/topics/nasalife/index.html