"Habitation of Mars has at least some novelty — but it too will soon wear off. Bases on asteroids or colonies out there in space? Forget it."

Well, if I have to forget the possiblity of opening a new frontier, and I am required to "settle" for exploration [meaning quenching various scientific *needs*]. Then I don't want my tax dollars spent supporting the NASA bureacracy- this activity simply is not worth 10 billion or more per year. Maybe it's worth a couple billion per year.
Of course, what the UK is spending related to space activity, fits Singer's model- actually Britian is fairly generous in this regards considering it's GNP.
The countries other than Britian, have a very different view. India, Japan, ESA, China, are not focused solely on entertaining some elite group of scientists.

I don't see the novelty of Mars habitation as important. I would rather we spend the billions on strengthen our battle against AIDS in Africa, or simply have more spending on various national security efforts. There are even possible ways to wisely spend money on social issues- put a few billion in this area and perhaps we get much better understanding at "how" we could spend money improving the human condition- instead of merely wasting globs of money in huge bureaucratic circle jerks. Simply stated there could be lots of other alternatives to spending tens of billion obtaining some novelty- lower taxes would also "work".
Now, I view space exploration which has the intention of opening up the space frontier is practical priceless- so fundementally altering our future that assigning any dollar amount is fairly meaningless: trillions, tens of trillions, billions of trillion. Look at the computer revolution, how do you measure this? And opening the space frontier, could utterly and completely dwarf this.

Now, of course, people who truely support a manned Mars mission are looking at a way to open up the space frontier. The real debate is HOW to you open this frontier. And I don't see the debate as between building a lunar base or a Manned Mars. The issue for me is when is NASA going to stop thinking it "rightfully" owns space, when is NASA going to become our space agency, when is NASA going start working with Americans in order to encourage space development?
And if NASA is inherently incapable of performing in accordance to it's charter; when is it going to be pushed aside or effectively sidelined, so that people who want to lead this effort can function without being hindered by NASA or any other alphabet soup govt agency.